A quick brush of saffron water and a sprinkle of sugar before baking give this buttery shortbread its crackled top and delicate floral flavor. Paired with a saffron-infused latte, it's a satisfying snack on a chilly fall afternoon.
Preheat oven to 325°F. Place saffron in a small bowl; add hot water and let stand 20 minutes. Brush an 8-inch round cake pan with butter. In a bowl, beat butter with confectioners' sugar on medium speed until light and fluffy, about 2 minutes. Add 1/2 teaspoon saffron water and vanilla; beat until combined, scraping down sides as needed. Add flour and salt; beat until just combined.
Pat dough evenly into prepared pan; refrigerate until firm, about 20 minutes. Crimp edges with a fork. Cut into 8 wedges with a sharp knife, and dock all over with a skewer or fork. Brush remaining saffron water over top; sprinkle with granulated sugar. Bake until firm and golden around edges, 30 to 35 minutes. Let cool slightly in pan on a wire rack, then turn out of pan, re-slice wedges with a serrated knife, and let cool completely. Shortbread can be stored in an airtight container at room temperature up to 1 week.