Mix butter, eggs, flour, baking powder, lemon juice and lemon rind, thoroughly. Use milk to make moist, less than 1/4 cup - dough will be soft. Roll out between wax paper and spread on cookie sheet (with sides).
Spread 1 1/2 pound lekvar on the dough.
Filling: Mix powdered sugar and egg yolks until well blended.Beat egg whites until stiff. Fold in walnuts to yolk mixture. Then fold in egg whites. Pour over lekvar.
Bake 30 minutes at 350 degrees. Edges will be beige. Cool and cut into small squares. Sprinkle powdered sugar on top.