Preheat oven to 350 degrees F. Lightly grease a 13x9 inch baking pan.
To Make the Crust, melt the butterscotch chips and butter in a medium saucepan, stirring until smooth. Remove from the heat and add in the graham cracker crumbs and walnuts. Spread 1/2 of this mixture evenly into the bottom of the prepared baking pan.
To Make the Filling, beat the cream cheese and condensed milk together in a medium bowl using an electric mixer. Add the egg and vanilla, mixing well. Pour the mixture over the crust. Sprinkle the remaining crust mixture over the filling.
Bake for 25 to 30 minutes, until a toothpick inserted in the center comes out clean. Cool in the pan on a wire rack before cutting into large or small bars.