Spray a 13x9 dish with non-stick cooking spray. Cook Italian sausage and onion in skillet over medium heat until browned; drain off fat. Add spaghetti sauce, tomato sauce, and spaghetti sauce mix in skillet over low heat. Add meat mixture to sauce. Chop pepperoni in fourths and add to skillet. Simmer 2 minutes.
Pour meat mixture in bottom of dish. Top with cubed Velveeta, mozzarella, and parmesan. Spread sour cream to cover cheeses. Pat out biscuits to cover meat/cheese mixture, seal biscuits at pan edges.