1 (4 oz.) pkg. shredded Mozzarella cheese
2 (4 oz.) pkgs. shredded Cheddar cheese
3 tbsp. prepared mustard
3/4 c. mayonnaise
3/4 to 1 c. grated green onion
1 French loaf bread
Pepperoni, if desired

Mix 2 cheeses, mustard, and mayonnaise together. Chop onion and slice loaf of bread. Spread thin layer of butter on bread. Add sliced pepperoni, add cheese mixture and sprinkle grated onion on top. Wrap each half in foil and bake in 300 degree oven for 20 minutes. Bake open-faced 1 minutes.