Preheat oven to 350 degrees
Crust: Beat the butter and cream cheese until smooth. Add flour and mix until a dough forms. Divide into 24 balls. With your fingers, press each ball into an ungreased mini muffin cup. Make sure the dough is smooth on the bottom and sides and doesn't hang over the top of the cup.
Filling: Whisk the egg in a medium bowl. Add sugar, butter, salt and walnuts; mix well. Add the filling to the crust so that it comes almost to the top of the crust.
Bake for 20 minutes at 350º then for about 10 minutes at 250 degrees. Cool before removing from muffin tins.
*note: ½ cup chocolate chips may be added