2 sticks (8 ounces; 230 grams) unsalted butter, at room temperature
2/3 cup (70 grams) confectioners’ sugar, sifted
2 large egg yolks, at room temperature
Pinch of salt
2 teaspoons tequila
Grated zest of 2 limes
Grate zest of half an orange
2 cups (280 grams) all-purpose flour
Coating:
Approximately 1/2 cup clear sanding or other coarse sugar
2 teaspoons sea salt
Put the butter in the bowl of a mixer fitted with the paddle attachment and beat at medium speed until it is smooth. Add the sifted confectioners’ sugar and beat again until the mixture is smooth and silky. Beat in 1 of the egg yolks, followed by the salt, tequila, grated lime and orange zest. Reduce the mixer speed to low and add the flour, beating just until it disappears. It is better to underbeat than overbeat at this point; if the flour isn’t fully incorporated, that’s OK—just blend in whatever remaining flour needs blending with a rubber spatula. Turn the dough out onto a counter, gather it into a ball, and divide it in half. Wrap each piece of dough in plastic wrap and refrigerate for about 30 minutes.
Working on a smooth surface, form each piece of dough into a log that is about 1 to 1 1/4 inches (2.5 to 3.2 cm) thick. (Get the thickness right, and the length you end up with will be fine.) Wrap the logs in plastic and chill for 2 hours.
Position the racks to divide the oven into thirds and preheat the oven to 350°F (180°C). Line two baking sheets with parchment paper.
While the oven is preheating, work on the sugar coating: Whisk the remaining egg yolk in a small bowl until it is smooth and liquid enough to use as a glaze. Mix the coarse sugar and flaky salt well and spread the mixture out on a piece of wax paper. Remove the logs of dough from the refrigerator, unwrap them, and brush them lightly with a little egg yolk. Roll the logs in the sugar, pressing the sugar/salt mixture gently to get it to stick if necessary, then, using a sharp slender knife, slice each log into cookies about 1/4 inch (7 mm) thick.
note: To get the sugar/salt mixture to stick better, I moved the log over to a piece of plastic wrap, and in the sort of technique you’d see a sushi chef use to shape a roll, use the plastic to press the sugar in by wrapping it tightly.] (You can make the cookies thicker if you’d like; just bake them longer.) Place the cookies on the lined baking sheets, leaving about 1/2 inch (1.5 cm) space between them.
Bake the cookies for 12 to 14 minutes, or until they are set but not browned. (It’s fine if the yolk-brushed edges brown a smidgen.) Transfer the cookies to cooling racks to cool to room temperature.
Keeping: Packed airtight, the cookies will keep for about 5 days at room temperature. Because the sugar coating will melt, these cookies are not suitable for freezing.