Preparation

Several hours or the day before baking:

• In a small bowl, combine the flour, poppy seeds, baking powder, and salt. With an electric mixer, beat the butter and sugar until light and fluffy. Add the egg, orange juice, orange zest, and lemon zest; beat until blended, scraping down the sides of the bowl. Add the flour mixture, beating on low just until combined. Scrape the soft dough onto a large piece of plastic wrap (about 13 inches long), wrap and freeze for 30 minutes.
• Unwrap the dough and knead it briefly on a floured surface to remove any air pockets. Wrap the dough in plastic again; roll and gently pull opposite ends of the wrapped dough to create a 9-inch-long log. Freeze the log for 1 hour or refrigerate for several hours until very firm. (The dough can also be kept frozen, well wrapped, for several weeks.)

To bake:

• Heat the oven to 350°F. Lightly grease your cookie sheets or cover them with parchment (the cookies will spread a bit more and be slightly crisper on greased sheets). Unwrap the log and roll it briefly on a lightly floured surface to remove the wrinkles on the dough’s surface and to make the log more evenly round. Slice the log crosswise into 3/16-inch-thick rounds. Set the rounds 1 inch apart on the cookie sheets. Bake until the edges are lightly browned, 12 to 14 minutes. Let cool for 5 minutes on the sheets; transfer to a wire rack to cool completely.