Combine zest of 1 medium orange and ¼ cup coarse white sanding sugar in a small bowl and rub together with your fingers until very fragrant and sugar is bright orange, about 2 minutes. Spread out on a rimmed baking sheet; let dry. (Drying takes at least 12 hours). Store in covered container until ready to glaze the cookies.

Beat ¾ cup (1½ sticks) unsalted butter, ½ cup (55 g) powdered sugar, 1 Tbsp. vanilla paste, and 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt in a large bowl until sugar is dissolved and mixture is smooth.

Add 1½ cups (188 g) all-purpose flour and mix until a soft dough forms and no pockets of dry flour remain. Form into disc and refrigerate at least 2 hours.

Place a rack in middle of oven and preheat to 325° convection. Roll dough on floured board to ¼-⅓” thickness, then cut shapes and place on parchment-lined baking sheet. Refrigerate for 30 minutes.

Bake shortbread, rotating pan halfway through, until edges are lightly browned, about 16 minutes. Transfer pan to a wire rack and let shortbread cool completely. Store unglazed as glazing softens the cookie.

Day of serving: Whisk ¼ cup fresh lemon juice, 3 Tbsp. pomegranate juice, and remaining 4½ cups (495 g) powdered sugar, ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt, and ½ tsp. vanilla bean paste or vanilla extract in a medium bowl until smooth. Glaze should be very thick but still slightly pourable (like thick honey). If it’s too thin, add more powdered sugar a tablespoonful at a time until the right consistency. (If not using immediately, cover with plastic wrap, pressing directly onto the surface, to keep from drying out.)

Working with 1 cookie at a time, dip top of shortbread into glaze (keeping sides unglazed), holding it above bowl to allow excess to drip back into bowl. Place, glaze side up, on a wire rack and immediately sprinkle generously with orange sugar. (Touch up glaze with an offset spatula before adding sugar if there are any bare spots. You might not use all of the glaze or orange sugar.) Let cookies sit 1 hour for glaze to set up before serving.