Step #1 These are nicely crisp & are very good with a fruit-based dessert.
Step #2 In a bowl, cream together the butter, the lemon & lime zests, preferably of an electric stand mixer, 1 c of the sugar, & salt.
Step #3 One at a time beat in the egg yolks; stir in the the lemon & lime juices.
Step #4 Add 2 1/2 c of the flour & mix until just mixd.
Step #5 Transfer the dough to a container & chill it for at least 2 hrs.
Step #6 (The dough can be prepared up to 3 days ahead & refrierated or frozen for up to 1 month.
Step #7 Defrost the frozen dough in the refrigerator before using.
Step #8 ) Position racks in the upper & lower thirds of the oven and preheat the oven to 375F.
Step #9 Grease several baking sheets.
Step #10 Working in batches, by rounded tbspfuls, measure out the chilled dough and form it into 1-inch balls.
Step #11 Place the balls of dough on the baking sheets, spacing them well apart.
Step #12 Use the remaining flour to coat the flat bottom of a glass or measuring c.
Step #13 Flatten the balls into 2-inch rounds about 1/4-inch thic, reflouring the glass a necessary.
Step #14 Bake the cookies, exchanging the position of the sheets on the racks from top to bottom & from front to back, for about 10 mins or until the cookies are crisp & the edges & bottoms are lightly colored.
Step #15 With a spatula, transfer the cookies as soon as possible to parchement paper & Sprinkle top with generously with the remaining 1/2 c of sugar.
Step #16 (The cookies can be baked 1 day ahead & stored in an airtight container.