Pre heat over to 350 degrees.
Prepare a 9x9 inch pan with baking spray.
Mix cake mix, oil, milk, and egg in large mixing bowl. Stir until well mixed.
Add in the candy melts and continue stirring. The batter will be very thick.
Spread evenly into baking pan.
Bake for 20 minutes. Check and continue baking for 5 additional minutes if needed.
Allow to cool completely before cutting into squares.