Preheat oven to 300°F. Cream butter and sugar well, add egg yolk and continue beating. Add lemon juice, lemon rind, and flour and continue beating until well blended.
Pat dough out 1/4 inch thick in a greased and floured 9-inch square pan. Brush with slightly beaten egg and sprinkle with nuts. Bake for 20 to 30 minutes. Cut while hot into squares or 1-1/2-inch strips.