Butternut Squash and Blue Cheese Bake - Easy Sunday Side Dish

A gorgeous, golden butternut squash bake with caramelised onions, sage, a creamy blended squash sauce and crumbled blue cheese on top. It sounds fancy, it looks incredibly impressive on the table, and this is about to become your new favourite Sunday side dish. Butternut squash is one of those vegetables that is SO cheap when it is in season, we are talking four dollars for a squash bigger than my head, and this recipe makes the absolute most of every single bit of it. Let's cook!

Why This Butternut Squash Bake Works

One squash does three completely different jobs. The bottom half is diced and roasted, then half of that is blended into the sauce and half is layered into the base. The top half is sliced thin and goes over the whole thing. Same vegetable, three textures, one dish.

The sauce is squash, not flour and butter. There is no roux here and no cream. Roasted squash blended with stock and milk thickens itself, which is why the bake tastes of vegetable rather than of white sauce.

The chicken stock is where the savouriness comes from. Squash is sweet and blue cheese is salty, and without something meaty underneath them the whole thing goes one-note. This is the ingredient people are most tempted to swap and the one I would keep.

Properly caramelised onions, not softened ones. Fifteen to twenty minutes on a low heat with a pinch of salt. This is the difference between a bake that tastes sweet and deep and one that tastes flat.

A mild blue, not a strong one. Strong blue cheese bulldozes the squash. A mild creamy one gives you the salty tang without taking the dish over.

Recipe Details

• Prep Time: 20 minutes
• Cook Time: 1 hour, including roasting and baking
• Total Time: 1 hour 20 minutes
• Serves: 6 as a side dish
• Difficulty: Easy
• Special Equipment: Air fryer or oven, blender or stick blender, small baking dish

The one thing that decides whether this works is how thinly you slice the top half. I have made it with slices that were too thick and the top layer stays firm in the middle while everything underneath is perfect, and no amount of extra time in the oven fixes it neatly, it just dries the edges out. Get them as thin as you can, ideally on a mandoline, and they cook through in the same time as everything else and go golden and slightly frilly at the edges. If you only have a knife, take your time. The other thing worth saying is that the diced squash for the sauce wants proper colour on it before it goes anywhere near the blender. Pale roasted squash makes a pale, sweet, slightly flat sauce. Golden edges make it taste roasted.

Ingredients

For the Roasted Squash

• 1kg butternut squash, divided, bottom half diced and top half thinly sliced
• 2 cloves garlic, left whole for roasting
• Olive oil, for roasting
• Salt and pepper, to season

For the Caramelised Onions

• 2 onions, thinly sliced
• 2 cloves garlic, finely chopped
• 5 large fresh sage leaves, finely sliced
• Olive oil or butter, for cooking

For the Sauce

• 600ml chicken stock
• 200ml milk
• Half the roasted diced squash
• Salt and pepper, to season

To Assemble

• The remaining roasted diced squash
• The caramelised onions
• The thinly sliced squash
• 80 to 100g mild creamy blue cheese, crumbled

How to Make Butternut Squash and Blue Cheese Bake

1. Prep the squash: Preheat your oven to 180C (160C fan / 350F / Gas Mark 4). Cut the butternut squash in half. Dice the bottom half into roughly 2cm chunks. Thinly slice the top half as finely as you can. The thinner the slices, the more evenly they cook and the more beautifully golden they turn on top. A mandoline makes this easy if you have one.
2. Roast the diced squash: Toss the diced squash and the 2 whole garlic cloves in olive oil, season well with salt and pepper, and roast in the air fryer at 200C for 15 to 20 minutes until soft and golden. Alternatively roast on a tray in the oven at 200C for 25 minutes. You want it tender all the way through with a little colour on the edges.
3. Caramelise the onions: While the squash is roasting, heat a pan over a medium to low heat with a drizzle of olive oil or a knob of butter. Add the sliced onions and a pinch of salt and cook slowly for 15 to 20 minutes, stirring occasionally, until they are deeply golden, soft and sweet. The salt helps them soften and caramelise beautifully. Add the chopped garlic and sliced sage for the last 3 to 4 minutes and stir through.
4. Make the sauce: Once the diced squash is roasted, add half of it to a jug or blender along with the chicken stock and milk. Blend until completely smooth. Taste and season well with salt and pepper. The sauce should be creamy, golden and absolutely gorgeous.
5. Assemble the bake: In a small baking dish, combine the remaining roasted diced squash and the caramelised onions. Pour the blended sauce over the top and give everything a gentle stir. Lay the thinly sliced squash over the top in an even layer, overlapping slightly as you go. Crumble the blue cheese generously over the top.
6. Bake: Cover the dish with foil and bake at 180C for 30 minutes. Remove the foil and bake for a further 10 minutes until the top is golden and the sliced squash is tender. If your slices are on the thicker side it may need another 5 to 15 minutes, so keep an eye on it. A knife should slide through the top layer with no resistance when it is done.
7. Serve: Leave it to rest for 5 minutes before serving. It is absolutely gorgeous straight from the dish, golden and bubbling and smelling incredible!

Why You'll Love This Recipe

• Incredible value: Butternut squash is one of the cheapest vegetables you can buy in season and this uses the whole thing
• It looks stunning: Golden layered squash with bubbling blue cheese, a proper showstopper side
• Nothing goes to waste: Diced for the base, blended for the sauce, sliced for the top
• Make ahead friendly: Assemble it in advance and put it in the oven when you need it
• Goes with everything: A Sunday roast, a dinner party, or anything that needs something special alongside

Chef's Tips for Butternut Squash and Blue Cheese Bake

Slice the top half as thinly as you can: This is the most important tip in the recipe. Thin slices cook evenly and go golden. Thick ones stay underdone in the middle. Use a mandoline if you have one, or take your time with a sharp knife.

Use a proper chicken stock: This is the backbone of the sauce and a stock cube dissolved in water will not do the same job. If you want the real thing for nothing, my Homemade Chicken Stock Cubes (From Food Waste!) are made from the carcass and vegetable scraps you were going to throw out anyway, and they freeze into portions exactly this size.

Do not rush the caramelised onions: Low and slow is the only way. Turning the heat up to hurry them gives you soft onions, not caramelised ones. The sweetness and depth they add is worth every minute.

Get real colour on the roasted squash: Especially the half going into the blender. Pale squash makes a pale, flat sauce.

Use a mild creamy blue: A strong blue will overpower the delicate sweetness of the squash. Go for something mild and creamy and you still get that gorgeous salty, tangy punch without it taking over.

Freeze your onions pre-sliced: Slice a big batch and keep them in a bag in the freezer. They go into the pan straight from frozen and caramelise just as well. A brilliant little time saver.

Make it ahead: Assemble the whole thing up to the point of going in the oven, cover it, and keep it in the fridge for up to a day. Add an extra 5 to 10 minutes to the covered baking time if it goes in cold.

Substitutions & Variations

• No blue cheese? Feta gives a milder, saltier finish, or goat's cheese for something creamy and tangy
• Vegetable stock: It will work and it makes the dish vegetarian, but you lose the savoury depth that balances the sweetness, so season it harder
• No sage? Fresh thyme or rosemary are both beautiful here
• Dairy free: Any milk works, including oat or almond, with a dairy free cheese alongside
• No butternut squash? Pumpkin works beautifully when butternut is out of season
• Make it a main: Serve with crusty bread and a green salad and it feeds 3 to 4 properly

Storage

Best eaten fresh: Straight from the oven when the top is golden and the blue cheese is still bubbling. That said, the leftovers are genuinely delicious the next day.

Fridge: Cover and store for up to 3 days. Reheat covered with foil at 160C for 15 to 20 minutes until hot all the way through.

Freezer: It freezes well for up to 2 months. Cool completely, cover tightly and freeze, then defrost overnight in the fridge before reheating in the oven.

Avoid: Do not microwave this one. The sliced squash on top steams rather than reheats and you lose all of that lovely texture. Always back into the oven.

Frequently Asked Questions

Can I use frozen butternut squash? Fresh is definitely best here, especially for the sliced top layer. Frozen diced squash can work for the base and the sauce, but it will not slice, so stick to fresh for the top.

Why chicken stock in a vegetable dish? Because squash is sweet and blue cheese is salty, and without something savoury underneath them the bake goes one-note. The stock is doing real work here, which is why it is not the first thing I would swap out.

My top layer isn't cooked through, what do I do? Cover it back up with foil and give it another 10 minutes. This almost always comes down to slice thickness, so go thinner next time and you will not have the problem.

Can I make this as a main rather than a side? Absolutely. Serve it with crusty bread and a simple green salad and it is a completely satisfying vegetarian main for 3 to 4 people, using vegetable stock.

I don't have an air fryer, can I roast the squash in the oven? Yes. Roast on a lined tray at 200C (180C fan / 400F / Gas Mark 6) for 25 minutes, tossing halfway through, until golden and tender.

Can I use pumpkin instead of butternut squash? Yes, any firm fleshed pumpkin works beautifully. Just make sure it is firm enough to slice thinly for the top layer. The Roasted Pumpkin and Lentil Salad with Tahini Dressing is another good one for the same glut.

How far ahead can I assemble it? Up to a day. Build it completely, cover it, and refrigerate. Give it an extra 5 to 10 minutes covered in the oven if it is going in fridge cold.

Can I double it? Yes, but use a wider dish rather than a deeper one. A deep bake means the top layer is golden long before the middle is hot.

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This butternut squash and blue cheese bake is one of those recipes that looks completely spectacular but is actually very straightforward to pull together. It is the kind of dish that earns you serious compliments at a Sunday table without costing a fortune or taking your whole day, and the make ahead options make it brilliant for dinner parties too. I genuinely hope it becomes a regular for you.

Enjoy!

Del x

Golden squash roasted two ways, deeply caramelised onions, a creamy blended sauce and bubbling blue cheese on top, all baked into the most show-stopping autumn side dish.