Melt the butter in a saucepan, then stir in the flour and cook for 1 minute. Gradually stir in the milk, then keep stirring until the mixture begins to bubble and thickens to a creamy sauce. Remove from the heat, then stir in all but a handful of the cheese.

Heat oven to 220C fan and bring a large pan of water to the boil. Cook the potato slices for 5 minutes, tip in the broccoli and cauliflower for another 3 minutes, then finally add the peas for 1 more minute. Drain all the veg. Reserve enough potato slices to cover the top of the dish, then gently stir the rest of veg into the sauce.

Tip into a deep ovenproof arrange over the reserved potato slices, then sprinkle with the remaining cheddar. Bake for 20-25 minutes until the top in golden and crisp.