In a large bowl, combine butter and cream cheese until smooth. Gradually add flour until blended.
Shape into 48 balls (1 in. each); press onto the bottom and up the sides of ungreased miniature muffin cups. Bake at 400° for 12-15 minutes or until lightly browned. Cool for 5 minutes; carefully remove from pans to a wire rack to cool completely.
For filling, in a large bowl, whisk milk and pudding for 2 minutes. Let stand for 2 minutes or until set. Cover and refrigerate for 5 minutes. Spoon into tart shells. Yield: 4 dozen.