Glossy Pretzel And Sea Salt Shortbread

Pulse the hard pretzels in a food processor until they form coarse crumbs. Stop before they turn into a fine powder to retain their crunchy texture.

In a stand mixer fitted with the paddle attachment, cream the room-temperature unsalted butter, granulated sugar, and powdered sugar on medium speed until light and fluffy.

Pour in the vanilla extract, then add the all-purpose flour, coarse pretzel crumbs, and fine sea salt. Mix on low speed until a cohesive dough just begins to form.

Turn the dough onto a work surface and shape it into a tight log approximately 5cm in diameter. Scatter the demerara sugar on the counter and roll the log over it until the exterior is evenly coated. Wrap tightly in plastic wrap and chill in the refrigerator.

Preheat the oven to 175°C (350°F). Line a baking sheet with parchment paper.

Using a chef's knife, cut the chilled dough log into rounds about 1cm thick. Arrange them on the prepared baking sheet, leaving 3cm of space between each.

Whisk the egg yolk and water together to create a simplified wash. Using a pastry brush, lightly paint the tops of the unbaked cookies to achieve the characteristic glossy surface, then sprinkle with flaky sea salt.

Bake at 175°C (350°F) for 14 to 16 minutes, or until the edges are deep golden brown and the glossy tops are set.

Remove from the oven and allow the shortbread to cool completely on the baking sheet. This resting period allows the butter structure to solidify, giving the cookie its characteristic snap.