Blend cake mix with melted butter/margarine and condensed milk. Spread 1/2 of the mixture into a greased 9 X 13 baking pan. Bake at 350 degrees for 10 minutes. Remove from oven. Slice unwrapped Snickers bars in half and lay these over the baked crust. Crumble the remaining batter over the top of the candy bars. (Note: It will have a crumbly texture so there is no need to try to smooth it out). Return to the oven and bake for another 30 minutes. Cool completely and cut into squares.