Makes about 5 dozen cookies
2 1/2 cups all-purpose flour, plus more for dusting
2 Tbl poppy seeds
½ tsp baking powder
½ tsp salt
2 stick butter, room temperature
1 1/2 cups granulated sugar, plus more for dusting
2 large eggs, plus 1 egg white
2 Tbl freshly squeezed orange juice
2 Tbl finely grated orange zest, packed (from about 3 large oranges)
2 tsp finely grated lemon zest (from about 1 lemon)
Note: The dough should be made several hours ahead or even the day before baking.
In a medium-sized mixing bowl, whisk to combine the flour, poppy seeds, baking powder and salt. Set aside.
Combine the butter and sugar in the bowl of an electric stand mixer fitted with the paddle attachment. Beat at medium-high speed until light and fluffy, about 3 minutes. Using a rubber spatula, scrape down the sides of the bowl and the paddle. Add the eggs (just the two whole eggs, not the whites), orange juice, orange zest and lemon zest. Beat until blended, then scrape the bowl again. Add the flour mixture and mix on low until just combined. Scrape the sides of the bowl again, then give one last stir.
Halve the dough. Shape each half into a long log. Lightly dust two sheets of parchment paper, then place one log on each sheet. Lightly dust the logs with flour, then roll in the parchment to a 1 ½ inch diameter, pressing a ruler along the edge of the log at each turn to narrow and shape the log. (This is really difficult to describe without a visual aid. Luckily, I’ve found one on the web. Check out this video from my alma mater. This ruler business comes at about 3:14.) Freeze until firm, at least 1 hour. (Remove the logs every ten minutes or so, during the first half hour, and lightly roll them on the countertop, to help maintain the round shape.)
Pre-heat the oven to 375°F. Arrange the racks in the upper and lower thirds of the oven. Line a few baking pans with parchment paper and set aside.
Using a fork, beat the egg white in a small mixing bowl. Place about ½ cup granulated sugar in a large plate. Lightly but evenly brush each log with the beaten whites, then roll the log in the sugar, to evenly coat its sides.
Slice each log into rounds of about 3/16-inch (just under ¼-inch) thickness with a sharp knife. To help maintain the round shape of the log and the resulting cookies, turn the log a little bit after each slice. (Each log should yield between 2 and 3 dozen rounds.) Space the rounds about 2-inches apart on the parchment-lined baking pans.
Bake, 2 pans at a time (and keeping the rest of the dough refrigerated), until the edges are golden, 10-15 minutes, rotating the pans (trading their positions and turning them each 180 degrees) about half-way thorough. Let cool on the baking pans, placed on wire racks. Cool completely to room temperature before storing at room temperature in air-tight containers, for up to 3 days.