##peel and finely dice onion##. Melt the fat in a pot. Fry diced onions in it until transparent. Add flour and sauté. Deglaze with stock and milk and simmer for about 5 minutes while stirring.
Meanwhile, grate ##cheese## Add cheese to the sauce and melt for 2-3 minutes while stirring. Season to taste with salt, pepper and nutmeg.