2 sticks (8 ounces) unsalted butter (preferably high-fat, like Plugra), softened at room temperature
1/2 cup granulated sugar
1/4 cup confectioners’ sugar, sifted before measuring
1/2 teaspoon salt, preferably sea salt
2 large egg yolks, preferably at room temperature
2 cups all-purpose flour.
zest of 1 lemon and zest of 1 lime
1 egg yolk
Crystal or dazzle sugar.