2 and 1/2 cups all-purpose flour
3/4 cup confectioners' sugar, divided, plus more, sifted, for rolling
1/2 teaspoon fine salt
2 sticks unsalted butter, room temperature
1 tablespoon grated lemon zest plus 1 tablespoon juice
1 tablespoon grated lime zest plus 1 tablespoon juice
1/3 cup fruit jam or citrus curd, for filling
Preheat oven to 325 degrees. Combine flour, 1/2 cup confectioners' sugar, and salt. In a large bowl, using a mixer, beat butter, remaining 1/4 cup sugar, and citrus zest and juice on medium until combined; increase speed to high and beat until pale and fluffy, 5 minutes. Beat in flour mixture on low. Roll rounded tablespoons dough into balls; place on a parchment-lined baking sheet. Freeze 10 minutes.
Bake 10 minutes. Remove from oven; with small end of a melon baller or a small rounded measuring spoon, make indents in centers of cookies. Return to oven, and bake until set and light golden at edges, 12 minutes more. Transfer cookies on parchment to wire racks, let cool 10 minutes. Gently toss in sifted sugar, then sift more sugar over tops. Fill centers with jams and curd.