Ingredients:
- 50g breadcrumbs
- 20g butter
- For the crumb topping:
- 150g Gruyu00e8re, grated
- u00bd tbsp Dijon mustard
- 120ml cream, at room temperature
- Salt and black pepper
- 250ml milk, at room temperature
- 60g plain flour
- 60g butter
- 2 onions, sliced
- 2tsp olive oil
- 220g Brussels sprouts, quartered
- 350g cauliflower, chopped into florets
- 300g broccoli, chopped into florets
Method:
- Preheat the oven to 180˚C/160˚C fan/gas mark 4.
- Bring a large pot of water to the boil. Add the broccoli, cauliflower and Brussels sprouts and cook for 2-3 minutes until the broccoli turns vibrantly green.
- Transfer the vegetables to a large bowl of ice water for two minutes, then drain and place in a large casserole dish.
- Heat the olive oil in a saucepan over a medium-high heat and cook the onions for 4-5 minutes until golden and soft, stirring occasionally.
- Reduce the heat to medium-low heat and add the butter. Once melted, gradually mix in the flour, whisking constantly. Continue cooking and whisking for 1-2 minutes.
- Gradually add the cream and milk, whisking constantly. Simmer for 4-5 minutes until the sauce thickens.
- Remove the saucepan from the heat and stir in the mustard, half of the Gruyère and some salt and black pepper to taste.
- Pour the sauce over the vegetables, then top with the remaining cheese.
- Melt the butter for the topping in a bowl and stir in the breadcrumbs until combined, then sprinkle over the casserole.
- Bake for 20-25 minutes until golden on top and bubbling around the edges.
