6 slices bread (preferably medium thickness, white or brown or mixed)
60g softened butter
1 medium leek, sliced and washed
225g cheese (Caerphilly was traditional but cheddar works as well)
2 size 2 eggs
.25 level tsp mustard
Salt and pepper
30g walnuts (optional)
Finely chopped spring onions
Spread with butter on one side of the bread. Make sandwiches of the leek and 175g of the cheese. Press the sandwiches firmly together. Cut each sandwich into 4 triangles and arragge with the points upwards in a shallow ovenproof dish.
Beat the eggs, mustard, seasoning and milk together. Strain over sandwiches and leave for 25 minutes.
Preheat oven to 160 degrees (326 f gas mark 3). Scatter remaining cheese and walnuts if using over the pudding and cook in oven for 45 minutes or until set with a crisp topping. Sprinkle with the chopped spring onion and serve.