Green bean casserole

Ingredients

• 50 gButter
• 2 tbspOlive oil
• 250 gChestnut mushrooms, sliced
• 500 gGreen beans, trimmed
• 50 gFlour
• 500 mlMilk
• To tasteSalt
• To tasteBlack pepper
• 100 gCrispy onions

Instructions

1. 1

   Cook the vegetables

   Melt 15 g of the butter with the olive oil in a large frying pan over a medium heat. Fry the sliced mushrooms for 10 minutes, until golden. Stir in the trimmed green beans and cook for 4 minutes, then remove the vegetables from the pan.

2. 2

   Make the sauce

   Preheat the oven to 200°C. Melt the remaining butter in the pan over a low heat until bubbling. Stir in the flour to make a paste, then gradually pour in the milk, stirring to create a smooth, thick white sauce. Season with salt and black pepper.

3. 3

   Combine and transfer

   Return the mushrooms and green beans to the pan and stir them through the white sauce. Transfer the mixture to an ovenproof dish.

4. 4

   Prepare onions

   For homemade crispy onions, toss very thinly sliced onions with a light dusting of plain flour and a pinch of salt. To fry them, shallow-fry in neutral oil over a medium-high heat for 2–3 minutes per batch, until deep golden, then drain on kitchen paper. To bake them instead, toss with a little oil, spread on a lined tray and bake at 200°C for 18–22 minutes, turning once, until crisp.

5. 5

   Bake the casserole

   Top the casserole with the crispy onions and bake for 25 minutes, until golden. Serve warm from the oven.

What is green bean casserole?

Green bean casserole is a baked dish of green beans in a creamy sauce, typically finished with a crisp onion topping. It is especially associated with American home cooking, where it is often served as a comforting side.

This version builds its sauce from a simple butter-and-flour roux, with mushrooms adding savoury depth. Baking brings the components together and gives the onion topping time to turn golden.

Nutrition and macros by portion

The nutrition label shows one serving as written: 1790 calories, 43g protein, 184g carbs, 99g fat.

The flour and green beans provide most of the carbohydrates, while butter, olive oil, milk and crispy onions contribute much of the fat. Milk, mushrooms and green beans supply some protein, but the dish is not especially protein-rich; serve it with a protein source and a fresh vegetable side to balance the plate.

Why mushrooms and green beans work

Mushrooms: Frying them until golden gives them a more concentrated, savoury flavour and helps drive off some of their moisture before they meet the sauce.

Green beans: The brief pan-cooking softens them a little while leaving them with enough structure to finish cooking in the oven.

Getting a smooth white sauce

Roux: Stir the flour into the bubbling butter until it forms a paste, so it can thicken the milk evenly.

Milk: Add it gradually and keep stirring as the sauce thickens. A steady addition helps avoid lumps and gives you control over the final consistency.

The texture to look for

Sauce: Aim for a smooth, thick coating rather than a thin liquid. It should cling to the vegetables before the casserole goes into the oven.

Topping: The onions should be crisp and golden. If making them from scratch, slice them very thinly so they can crisp during the short frying time or the longer bake.

Timing the bake

The oven is set to 200°C, and the assembled casserole bakes for 25 minutes. Keep an eye on the topping towards the end: it should turn golden without becoming too dark.

The vegetables and sauce are cooked on the hob first, so the oven stage mainly heats the casserole through and finishes its surface.

Serving ideas

Serve the casserole warm, straight from the oven, while the topping is still crisp. It pairs well with roast potatoes, a simple salad or other roasted vegetables.

For a more substantial plate, serve it alongside roast chicken or another protein. If it is part of a larger meal, its creamy sauce and crisp topping make it a rich side.

Recipe notes & tips

• Slice the mushrooms evenly so they cook at a similar rate.
• Let the mushrooms turn golden before adding the green beans.
• Pour the milk in gradually while stirring to help keep the sauce smooth.
• Use an ovenproof dish that gives the casserole enough room for an even layer.
• Add the crispy onions just before baking so they sit on top rather than getting mixed into the sauce.

Variations

• Add garlic: Stir a little finely chopped garlic into the mushrooms as they cook.
• Use mixed mushrooms: Replace some of the chestnut mushrooms with another variety for a different savoury flavour.
• Make it vegetarian: Check that the crispy onions and any frying oil are suitable for your needs.
• Add mustard: Stir a small spoonful into the finished white sauce for a sharper flavour.
• Homemade topping: Prepare thinly sliced onions using either the frying or baking method in the recipe.

Common mistakes to avoid

• Pale mushrooms: Give them time to brown before adding the beans, rather than crowding or stirring them constantly.
• Lumpy sauce: Add the milk in stages and stir thoroughly between additions.
• Thin sauce: Let it thicken on the hob before combining it with the vegetables.
• Soft topping: Keep the crispy onions on the surface and avoid covering the dish while it bakes.
• Overcooked beans: Cook them for the stated 4 minutes before baking; they will continue to soften in the oven.

How to store

Refrigerate leftovers in a covered container for up to 3 days. Reheat in an oven until piping hot; the onion topping may soften, so add fresh crispy onions if you want to restore its crunch.

Frequently asked questions