Pre-heat the oven to 220C / fan 200C / gas 7. Slice the potatoes into rounds. Cut the broccoli and cauliflower into small florets.
2
Melt the butter making sure it doesn’t burn, then add the flour and mustard powder. Stir for 1 minute.
3
Gradually stir in the milk until it makes a creamy sauce with no lumps.
4
Whilst making the sauce, boil a pan of water. Cook the potatoes for 5 minutes, then add the broccoli and cauliflower for an extra 5 minutes. Finally, add the peas.
5
Take everything off the heat. Drain the veg and add most of the cheese to the creamy sauce, leaving some for the top.
6
Place the remaining veg in a deep dish, add the sauce and snip in the chives. Mix it all together.
7
Layer the sliced potatoes on top and sprinkle the remaining cheese.