Wipe dirt away from the mushrooms, don't wash them under running water, they will become soggy. Chop the mushrooms.
Cook the chopped leeks first in some olive oil and butter till they're translucent but not too soft. Add the chopped mushrooms and stir till they're cooked. Season with salt and pepper.
In four ramekins, first pour some cream at the bottom. Ladle the mushrooms and leeks and divided the portions evenly.
Top with some cheese. Crack and egg to cover the top and pour on a little more cream.
Bake in a 180C pre-heated oven for 20 - 30 mins or till the egg is just about cooked but the yolk still runny.
Just before serving, drizzle a little truffle oil on each pot, you don't need a lot, like less than a teaspoon will do. If you don't have truffle oil, just drizzle some good olive oil instead.
Eat with bread or just as it is.