1. Preheat the oven to 350 degrees F. Lightly grease a 13 x 9 x 2-inch baking pan.
2. With an electric mixer stir together the butter, cake mix and 1 egg. Spread into the greased pan and pat down.
3. Still using an electric mixer, beat the cream cheese until smooth. Beat in the eggs and vanilla. Add the confectioners' sugar and beat well. Reduce the speed and slowly pour in the butter. Mix well. Fold in the toffee bits. Pour over the cake mixture.
4. Pour filling onto cake mixture and spread evenly. Bake for 50 minutes. Don't be afraid to make a judgment call on the cooking time, because oven temperatures can vary. You want the center to be a little gooey, so don't bake it past that point!