Step 1

Preheat the oven to 180°C. Grease a medium-sized oven-proof dish with butter.

Step 2

Melt the remaining butter in a large frying pan and gently cook the chopped leek until tender. Season with salt and pepper.

Step 3

In a large bowl, whisk together the eggs, cream and mustard. Season with salt and pepper.

Step 4

Slice the potatoes into thin discs.

Step 5

Line the base of the dish with half of the potatoes and layer with the ham, leeks, half the cheese and remaining potatoes.

Step 6

Pour over the egg mixture and top with remaining cheese.

Step 7

Cover with foil and bake for 1 hour, removing the foil for the final 10 minutes to brown the top slightly.