Green bean casserole is a Thanksgiving staple. Casserole in the USA doesn't quite mean the same as it does in the UK. In England, it generally refers to a bit of meat slow-cooked in liquid, more like to a stew. In the US it translates as any dish cooked in a casserole dish in the oven, often with a crispy, crunchy or cheesy topping. This green bean casserole is just that. A deliciously warming combination of a rich white sauce, flavoured with mustard and sour cream, tender green beans and crispy fried onions. Once you've tried it it's sure to become a firm family favourite, it's absolutely delicious.
- 600g green beans, trimmed and strung
- 200g sour cream
- 2 tbsp yellow mustard, we used French's
- 300g chestnut cap mushrooms, sliced
- 4 tbsp crispy fried onions, we used French's
- 425ml milk
- 25g plain flour
- 40g unsalted butter
- 2 bay leaves
- 1 small sprig thyme
- 2 cloves garlic, crushed
- 1 small onion, peeled and halved
- 4 black peppercorns
- 1 egg yolk
- Juice of 1 lemon
Preheat your oven to 180°C.
Bring the milk to a boil with the halved onion, bay leaves, garlic and peppercorns, turn off the heat and allow to steep for 10 minutes to infuse the flavours, strain into a jug whilst still warm and reserve.
Blanch the green beans in boiling salted water until barely cooked, you want plenty of bite to remain, drain and refresh in iced water to keep their colour. Drain again and shake dry, place in a buttered casserole dish.
Slice the mushrooms and sauté until golden brown in olive oil and place in a bowl to one side for later.
Over a low heat add the butter to a saucepan to melt. Add in the flour and stir with a wooden spoon to make a smooth paste, a roux, and continue to stir and cook this over a low/medium heat for 5 minutes, you want it to lose its raw flour taste without browning the flour. Now bit by bit, stir in the milk with a wooden spoon in stages and continue to stir briskly until the sauce is smooth. Bring up to a simmer, stirring all the while and cook until the sauce is thickened and has lost its floury taste, about 8-10 minutes. Be careful it doesn’t burn and stick. Remove from heat and beat in the egg yolk. Taste and season with lemon juice, salt and freshly ground black pepper to your liking.
Now whisk the sour cream and mustard through the white sauce. Add in the mushrooms and half of the crispy onions and stir.
Pour the sauce over the green beans in the casserole dish, bake in the oven for 15-20 minutes or until starting to bubble to a golden brown. Remove from the oven and veil the dish with the remaining crispy onions. Return to the oven for 5-10 minutes or until the whole dish is bubbling and piping hot.