Coat a 15x10x1-inch baking pan with some cooking spray.
In a medium mixing bowl, beat the cake mix, softened butter, and 1 egg with an electric mixer on low speed until mixture is crumbly. Pat into the bottom of the pan; set aside.
In a medium mixing bowl, combine cream cheese, the 2 eggs, and butter flavoring, if you like, and beat until smooth. Add the powdered sugar and beat on low speed until well combined. Spread on top of crust in pan.
Bake the bars in a 350 degree F oven for 25 to 30 minutes or until the filling is set and golden brown. Cool in pan on a wire rack. (The filling will fall when its cooled.) Cut into the bars. Garnish with cranberries and fresh mint leaves, if you like.