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.)