Buttery, tender-crisp shortbread with a subtle sourdough tang, perfect on their own or dipped in silky semi-sweet chocolate. Simple pantry staples transform into an elegant, lightly crunchy treat.
Cream the softened unsalted butter and granulated sugar in a stand mixer until light and well combined.
Add vanilla extract, salt, and sourdough discard; mix until fully incorporated, scraping down the bowl as needed.
With the mixer on low, gradually add the all-purpose flour and mix just until a soft dough forms (do not overmix).
Shape the dough into a rectangular brick about 12 inches long, 3.5 inches wide, and 1 inch high. Cut the brick in half and wrap both pieces tightly in plastic wrap.
Refrigerate for at least 1 hour (or long ferment 12–72 hours for deeper flavor and easier digestion).
Preheat the oven to 350°F and line a baking sheet with parchment paper.
Slice the chilled dough into 24 cookies, each about 1/2 inch thick. Arrange on the prepared sheet, spacing about 1 inch apart.
Bake at 350°F for about 10 minutes, until lightly golden at the edges.
Cool on a wire rack until set.
Optional: Melt semi-sweet chocolate in a double boiler and dip a corner of each cooled cookie. Place on a rack to allow chocolate to set before serving.