Boil pasta in a large pot of salted water; cook according to packet directions; drain.
In the meantime, heat the milk in a saucepan, but make sure it does not boil.
In a large pot melt 6 Tbsp. of butter and add the flour. Cook over low heat for 2 minutes, stirring constantly with a whisk. Add the hot milk (keep whisking) and cook for a couple of minutes until it becomes thick and smooth.
Remove from the heat and add the gruyere, cheddar, nutmeg and a sprinkle of salt and pepper. Stir well until evenly incorporated.
Place the mixture in 6-8 individual gratin dishes.
Melt 2 Tbsp. of butter and mix with the breadcrumbs and a pinch of paprika and sprinkle on top of each dish.
Bake for approximately 30 minutes, or until the top has turned golden-brown.