In a mixing bowl, blend together the butter and cream cheese until well incorporated. Add the flour, sugar, and salt, blending well. Gather dough and divide into two balls. Refrigerate in plastic wrap for at least 1-2 hours. Meanwhile, make the filling. In a bowl, mix together the sugar, cinnamon, salt, and chopped walnuts. When dough is chilled, cut each ball into two pieces. You will have 4 dough balls to work with.