Cream butter and sugar. Beat egg yolks and add with lemon extract and nuts. Gradually add the flour, beating well after each addition.
Beat egg whites until stiff and fold into mixture. Spread the dough about ¼ inch thick on a greased cookie sheet. Sprinkle with a topping as follows:
Mix all ingredients thoroughly and sprinkle over the cookie dough.
Bake in a preheated 350° oven 8 to 12 minutes. Take from oven and cut into squares while still warm.