Preheat oven to 325°F. Spray a 24-well madeleine pan with baking spray with flour.

In a large bowl, whisk together granulated sugar, zest, and eggs. In a medium bowl, whisk together flour, baking powder, and salt. Add flour mixture to sugar mixture, stirring just until combined. Add melted butter and vanilla in a slow, steady stream, whisking constantly, until combined. Cover and refrigerate until completely cooled, at least 2 hours.

Spoon batter by teaspoonfuls into prepared pans. Bake until madeleines spring back when pressed, 10 to 15 minutes. Let cool in pans for 5 minutes. Tap madeleines out onto a baking sheet lined with parchment paper. Sift confectioners’ sugar over warm madeleines, and serve immediately