Heat nonstick pan on low-medium heat. Melt a slice or two of butter.
Meanwhile in a microwave safe dish, heat 1-2 tablespoon of Mozzarella and ¼ cup-ish of Cheddar in the microwave. 30 seconds, stir, then 15-30 more seconds.
Spread cheese onto bread slices, then put into pan with melted butter. Fry for 2-4 minutes on each side, slice, and serve!