Cream butter and sugar; add yolk and lemon juice and beat well. Stir in flour until well blended.
Form into 1 inch balls, dip into beaten egg white then into chopped nuts. Place on greased cookie sheet, make deep indentation in center of each cookie. Bake for 5 minutes, then quickly indent centers again, continue baking for 10 minutes.
Fill center of each hot cookie with raspberry jam or jelly.
