Cheese sauce: Melt the butter in a saucepan. Fry the leeks and garlic for a minute without adding color. Sprinkle the flour over the onion and stir. Add the milk, a little at a time, and 2 cups of cheese, stir. Lower the heat and simmer for about 5 minutes, salt and pepper. Stir every now and then. Season with salt and pepper.
Cut broccoli into small bouquets and the stalk into thin slices. Boil water in a saucepan, add broccoli and cook for about 2 minutes. Put the pasta in a gratin form together with broccoli and sun-dried tomatoes.
Pour the sauce over the pasta and top with grated cheese and feta cheese. Grate high in the oven for about 10 minutes, until the gratin has become colored. Top with chopped parsley and freshly ground black pepper.