Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper and set aside.

In a large mixing bowl, combine the granulated sugar and lemon zest. Rub the zest into the sugar with your fingers until fragrant and slightly moist. This releases the natural lemon oils for more flavor.

Add the flour, baking powder, and salt to the lemon sugar. Whisk until evenly combined.

Add the very cold, grated butter. Using a pastry cutter or your fingers, gently work it into the flour until the mixture resembles coarse crumbs with small pea-sized pieces. These butter pockets are essential for creating flaky layers.

In a separate bowl, whisk together the egg, sourdough discard, lemon juice, milk, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and gently fold until a shaggy dough forms. Avoid overmixing to keep the scones tender.

Turn the dough onto a lightly floured surface and gently shape it into a rectangle. Fold it over onto itself 3–5 times, then gently pat it back into a rectangle. This layering of butter creates tall, flaky scones.

Pat the laminated dough into a disc about 8 inches (20 cm) in diameter.

Refrigerate the dough disc for 20–30 minutes to firm up the butter and make cutting easier.

Remove the chilled dough and cut into 8 equal wedges using a sharp knife or bench scraper.

Bake for 25 minutes, or until the tops are golden brown and the scones are set.

While the scones bake, whisk together the powdered sugar, vanilla, and 2–3 tablespoons (30–45 g) of fresh lemon juice until smooth. Adjust the consistency with more lemon juice or powdered sugar as needed.

Drizzle the lemon glaze over the warm scones once slightly cooled. Serve immediately or at room temperature.