Pizza Casserole - cooking recipe

Ingredients

1 (4 oz.) pkg. sliced pepperoni
1 medium onion, chopped
1/3 c. butter, melted
6 oz. thin spaghetti, cooked for 10 minutes
1 c. (4 oz.) grated Swiss cheese
1 lb. Mozzarella cheese, sliced thin
2 (8 oz. each) cans tomato sauce
1 (4 oz.) can mushrooms, drained
1/2 tsp. oregano (dry)
1/2 tsp. basil (dry)

Preparation

Boil pepperoni to remove excess fat for 5 minutes in water to cover, then drain well.
Saute onion in 1 1/2 tablespoons butter until golden brown.