Egg gratin with mashed potatoes

INGREDIENTS

* 500 grams of potatoes

* 100 grams of butter

* 125 ml of cream

* 2 leeks

* 50 grams of flour

* 100 ml of water

* 500 ml of milk

*Salt

* 100 grams of cheese

*Pepper

* 4 eggs

* A teaspoon of vegetable oil

INSTRUCTIONS