Wash the leeks and cut into thin rings. Heat a small amount of butter in a large pan over medium heat. Sauté the leek rings for 3-4 minutes until slightly softened. Cut the ham into strips and add to the pan, cooking for 2 minutes. Dust the flour over the mixture and stir well. Add the crème fraîche and cream, stirring until combined. Continue cooking over medium heat for 8-10 minutes until the leek is tender and soft. Season with salt and pepper to taste.
In a separate pan, heat a small amount of butter over medium-high heat. Cut the maultaschen into strips and fry for 5-7 minutes, stirring occasionally, until crispy and golden.
Preheat the oven to 180°C (350°F). In a greased baking dish, layer the crispy maultaschen strips and leek mixture alternately. Sprinkle the grated cheese over the top. Bake for 20-30 minutes until the cheese is melted and lightly golden.
This recipe makes enough for a small baking dish; to make enough for a larger dish, double all ingredient amounts.