Cook the pasta according to the package instructions and then strain them. Blanch the spinach for 2'-3', drain it and pour it in the pasta. Stir them gently.
Mix all the cheeses in a bowl. Place the pasta with spinach in an ovenproof baking dish, add the cheeses, pour the sour cream and sprinkle with breadcrumbs. If you want, you can sprinkle the top of the mixture with some more yellow cheese.
Bake the pasta in a preheated oven at 180° C (356° F) for 20-25'.