Place butter and granulated sugar in the bowl of a stand mixer fitted with a paddle attachment; beat until fluffy. Add egg and 1 yolk; mix until smooth. With the motor running, slowly add dry ingredients; beat until a smooth, stiff dough forms. Form dough into an 8” long tube, about 1 3⁄4” thick; wrap dough in plastic wrap and let sit at room temperature for 1 hour.
Heat oven to 350°. Unwrap dough; cut dough crosswise into twelve 1⁄2” pieces. Working with one piece dough at a time, roll dough into a 9” rope, about 1⁄2” thick. Transfer rope to a parchment paper-lined baking sheet, and keeping the center of the rope on the paper, pick up both ends, cross one end over the other, and twist; attach each end to the sides of the pretzel. Whisk remaining yolk with 1⁄2 tsp. water in a bowl; lightly brush cookies and sprinkle with sanding sugar. Bake cookies until golden, 12 minutes. Let cookies cool completely before serving.