In a bowl, cut butter into cake mix until the mixture resembles coarse crumbs. Pat into a greased 13-in. X 9-in. X 2-in. Baking pan. In another bowl, beat egg yolks; add the sour cream and mix well. Set aside 6-8 peach slices for garnish. Cut remaining peaches into 1-in. Pieces; stir into the sour cream mixture. Spread over crust; sprinkle with cinnamon. Bake at 350 degrees for 25-30 minutes or until the edges begin to brown. Cool on a wire rack. Spread with whipped topping; garnish with reserved peaches. Store in the refrigerator. Yield: 12 servings.