Cream butter. Add sugar gradually and cream until light. Add egg yolk,
mix thoroughly and blend in flour. Form into small balls about 1 inch in
diameter. Dip into egg white - then into nuts.
Place on greased cookie sheet and press fairly flat with bottom of glass.
Bake in slow oven, 350 degrees for 5 minutes. Remove from oven - press
centers down and bake about 15 minutes longer.
Cool and fill with tart jelly or jam such as lingonberry or currant
Makes 15 to 18 cookies.