Preheat the oven to 350 degrees F (175 degrees C).

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 a greased cookie sheet, make a deep indentation in the 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.