- Preheat the oven to 180°C/gas 4. Heat the olive oil in a pan, add the onion and cook for 4 minutes until softened, not browned.
- Add the plain flour to coat the onion, mix in a good pinch of white pepper and the wholegrain mustard. Slowly stir in the milk until it thickens.
- Add half the Cheddar and half the Parmesan, stirring for 2–3 minutes until melted. Meanwhile, boil the sprouts in boiling water for 7–8 minutes.
- Drain, place in an ovenproof dish, pour over the sauce, and top with wholemeal breadcrumbs and remaining Cheddar and Parmesan. Bake for 12–15 minutes, until golden brown on top.
- For extra flavour, add 2–3 cloves crushed garlic or 1 tbsp freshly chopped herbs, such as coriander or chives.
- Add 150g button mushrooms or a chopped leek to boost the veg count of this dish.
- For a festive feel, add 150g vacuum-packed cooked chestnuts.
- Freezing instructions: Defrost in the fridge or in the microwave then reheat until piping hot throughout.