Cream butter and cream cheese together. Add egg, vanilla; then mix in the flour. Cover and chill for a few hours to overnight. Roll out on lightly floured board to 1/4" thickness and cut with round cookie cutters. Place them on a cookie sheet as you would cookies. Use thumb to make indentation in center of each. Fill with about 1 tsp of desired filling. Bake at 350 F until lightly golden, about 10-15 minutes (guessing here, I just do it by sight).
Makes enough for a whole house of hungry Polish people at Christmas or Easter time!