In a bowl, cut butter into cake mix until crumbly. Add egg and mix
well. Press into a greased 13x9x2" baking pan. In a mixing bowl,
beat cream cheese and sugar. Add eggs and vanilla; beat until
smooth. Spread evenly over the crust. Bake at 350 F for 30 minutes.
Reduce heat to 325 F; bake 10 minutes longer. Dust with
confectioner's sugar while warm. Cool to room temperature before
cutting.