Preheat the oven to 190°C.
In a pan, add the leeks, cover with water and cook for six minutes until soft. In a bowl beat together the goat's cheese, 100g of the Parmesan cheese, sour cream and eggs.
Grease a gratin dish and add the tomatoes and leeks, pour over the cream mixture and top with the four slices of goat's cheese and the breadcrumb, Parmesan mixture. Place in the oven and bake for 25 minutes until brown and crisp.