Here is the recipe for Lemon Shortbread Cookies...
(Based on the Basic Shortbread Recipe I found.)
2 sticks butter, softened to room temperature
1 C super-fine (baker's) sugar
½ tsp salt
1-2 whole lemons, depending on size
1 lg egg yolk
1 lg whole egg
2 tsp vanilla
2 ¾ C flour
Decorative sugar (optional)
Take lemon and using a zester or small-holed grater, zest lemon peel. (Be careful to only obtain the colored part of the peel, do not go into the white part of the lemon's skin.) Peel should yield about 2 tsps of zest. (If your grater does not yield that much, you may need to zest a second lemon in order to make up the difference.)
Cut lemon in half, and using a strainer to catch the seeds, squeeze lemon halves for the juice. Should yield about 2-3 tablespoons. Cream butter, sugar, salt, and zest at high speed. Add yolk, beat another minute, add whole egg, beat again another minute. Add vanilla and lemon juice, beat again. Add flour, beat on low until dough has been mixed thoroughly and starts to cling to the paddle. Remove, divide in half. Roll half the dough into a log, about 1½ in diameter, repeat with remaining dough. Wrap each log in plastic and place in freezer. Freeze for at least 1 hour or until firm. (Can be stored in the freezer for up to 2 months.)
When logs are firm, take out 10-15 minutes ahead of time to thaw a little while oven heats up. Preheat oven to 325°F. Slice dough into ½- to ¾-in thick pieces and place slices onto parchment paper-lined cookie sheets.
If desired, sprinkle a little yellow decorative sugar on top.
Bake for 19-20 minutes; do not overbake to the point where the edges start to brown or else cookies will end up hard and tough.
Yields approximately 40-50 cookies, depending on thickness of slices.
For other variations on the basic cookie recipe, see also the Chocolate Shortbread and Almond Shortbread versions.