Wash leeks thoroughly to remove all dirt. Slice in half vertically down the leek.

Lay leeks cut side up and pour stock over them.

Sprinkle with salt and pepper.

Bake at 350, covered with foil (I take a cookie sheet and put it over the pan) for about 30 minutes. Sprinkle cheeses over top, dot with butter. Place under the broiler until the top is golden brown, 2-3 min.