Step 1

Preheat the oven to 390F / 200C.

Step 2

Melt the butter in a large frying pan or saucepan, then cook the onions slowly for about 10 minutes or until soft and beginning to caramelize.

Step 3

Add the mushrooms to the onions in the pan and cook for a further couple of minutes.

Step 4

Grease a standard quiche dish (or other round pan) with a little butter, then spread the onions and mushrooms evenly over the bottom. Scatter over the chopped ham and cheese.

Step 5

Slowly add the milk to the flour in a large jug. Whisk continuously so that there are no lumps, then whisk in the eggs, mustard, and salt and pepper.

Step 6

Pour the egg mixture over the fillings in the dish/pan, then bake for 30 (to minutes or until the mixture is just cooked in the centre. Slice and serve!