Cream butter with lemon peel and juice; add sugar gradually, beating until fluffy.
Add egg and 1 egg yolk, beating thoroughly after each addition.
Add a mixture of flour and salt in fourths, mixing until well blended after each addition.
Chill dough thoroughly, at least 1 hour.
Roll a third of dough at a time about 1/4 inch thick on a floured surface; cut with fancy cookie cutters.
Transfer to lightly greased cookie sheets; brush tops with beaten egg yolk.
Bake at 375Â°F 10 to 12 minutes.