Chocolate Hamantaschen

In a medium bowl, whisk together flour, baking powder, and salt. In another bowl, beat butter and sugar on medium speed until light and fluffy, about 3 minutes. Beat in orange zest and vanilla, then add 2 eggs, 1 at a time, scraping down bowl as necessary.

Reduce speed to low and gradually beat in flour mixture until combined. Add finely chopped chocolate and beat until just combined. Form dough into three 1-inch-thick disks, wrap tightly in plastic, and chill until firm, at least 1 hour and up to 3 days.

On a floured work surface, roll out dough to a scant 1/4-inch thickness. With a 2 3/4-inch round cutter, cut out circles; place on parchment-lined baking sheets. Gather scraps, chill, and repeat.

Whisk together remaining egg and 1 teaspoon water in a bowl. Brush circle edges with egg wash. Place 1 rounded teaspoon coarsely chopped chocolate in center of each circle. Lift sides of dough toward center, over filling, to form a triangle; pinch seams together. Freeze until firm, about 30 minutes. Preheat oven to 350 degrees with rack in center.

Bake cookies, 1 sheet at a time, until golden, 12 to 15 minutes. Let cool 5 minutes, then transfer to wire racks to cool completely.