Hamantaschen

Special equipment: a 3- to 3 1/2-inch round cookie cutter (the top of a wine or drinking glass also works well)

For the cookies: Preheat oven to 375 F. Whisk together flour, baking powder, lemon zest, and salt in a bowl.

In the bowl of an electric mixer, beat together butter and sugar at medium speed until light and fluffy. Add eggs, one at a time, until incorporated, then beat in vanilla. Scrape down sides of bowl and add flour. Mix on low speed until a dough just comes together. Gather dough into a ball and flatten into a disk. wrap tightly in plastic wrap and chill until firm, at least 3 hours or overnight.

Line a large baking sheet with parchment paper. Arrange racks in the middle of the oven.

Halve dough, and keep remaining half chilled. On a lightly floured surface, roll dough with a floured rolling pin to 1/4-inch thickness (about 10 inches round), dusting surface with flour as necessary. Cut out as many rounds as possible and transfer to baking sheet, arranging them 1/2 inch apart. Re-roll scraps and cut out more rounds. Put 1 teaspoon filling in center of each round and fold up edges to form a triangular shape, pinching corners together tightly but leaving filling exposed.

Bake until pale golden, 15 to 18 minutes. Cool on baking sheet on a rack 5 minutes before transferring cookies to rack to cool completely. Make more hamantaschen in the same manner on cooled baking sheet lined with parchment.

Make ahead: Dough can be made 2 days ahead and kept chilled, tightly wrapped. Cookies will keep in an airtight container at room temperature for up to 5 days.

For the Prune Filling: Combine prunes, water, sugar, and cinnamon in a small heavy saucepan. Simmer, covered, 20 minutes. Transfer mixture to a food processor, add lemon juice, then puree until smooth. Transfer to a bowl and chill completely.

Prune filling can be made, kept covered and chilled, for up to 1 week.