8 oz Unsalted butter, softened
1 1/2 c  Sugar
2 tb Minced lemon zest
2 tb Minced lime zest
1/4 ts Salt
4    Egg yolks
3 tb Fresh lemon juice
3 tb Fresh lime juice
3 c  Unbleached all-purpose flour
- (approximately)

These are nicely crisp and are very good with a fruit-based dessert.

In a bowl, preferably of an electric stand mixer, cream together the
butter, 1 cup of the sugar, the lemon and lime zests, and salt. One at a
time beat in the egg yolks; stir in the lemon and lime juices. Add 2 1/2
cups of the flour and mix until just combined. Transfer the dough to a
container and chill it for at least 2 hours. (The dough can be prepared up
to 3 days ahead and refrierated or frozen for up to 1 month. Defrost the
frozen dough in the refrigerator before using.) Position racks in the upper
and lower thirds of the oven and preheat the oven to 375F. Grease several
baking sheets. Working in batches, by rounded tablespoonfuls, measure out
the chilled dough and form it into 1-inch balls. Place the balls of dough
on the baking sheets, spacing them well apart. Use the remaining flour to
coat the flat bottom of a glass or measuring cup. Flatten the balls into
2-inch rounds about 1/4-inch thic, reflouring the glass a necessary. Bake
the cookies, exchanging the position of the sheets on the racks from top to
bottom and from front to back, for about 10 minutes or until the cookies
are crisp and the edges and bottoms are lightly colored. With a spatula,
transfer the cookies immediately to parchement paper and sprinkle with
generously with the remaining 1/2 cup of sugar. (The cookies can be baked 1
day ahead and stored in an airtight container.)