Prep: Preheat your oven to 425 F (220 C). Line a 18 by 13 inch baking sheet with parchment paper, and set aside.
Make the scone dough: Whisk together the egg and milk in a large glass measuring cup, until completely combined. Set aside 3 tablespoons of the mixture (for glazing your scones).
150 g buttermilk, 1 egg
Add the sourdough discard into the egg mixture and stir until no traces of sourdough remain. Set mixture aside.
113 g sourdough discard
In a large mixing bowl, whisk together flour, baking powder, salt and sugar.
300 g all-purpose flour, 14 g baking powder, 3 grams kosher salt, 30 grams granulated sugar
Rub the butter in by hand or with a pastry cutter until the mixture resembles fine breadcrumbs.
56 grams unsalted butter
Make a well in the center of the flour mixture, and pour in half of the milk mixture. With a large open hand gently mix the ingredients together until a shaggy dough forms. Add the remaining milk mixture and incorporate any leftover dry bits of flour.
Knead: Turn the dough out onto a clean surface and fold the dough on itself 4 or 5 times or until no traces of dry flour remain. Use a light hand and don't overwork the dough, but make sure the dough is cohesive and well incorporated and not crumbly.
Shape: Turn the dough out on a lightly floured work surface. Using your hands, flatten the dough out into an 8-by-10 inch rectangle, about 1 inch thick (the size doesn't have to be exact).
Using a 3-inch biscuit cutter, cut 6 scones and transfer them to prepared baking sheet.
Re-roll the dough lightly and cut 2 more scones. Transfer the dough to the baking sheet.
Bake: Brush the top of the scones with reserved milk and egg mixture.
Bake scones for 10 minutes at 425 F (220 C) and then reduce oven temperature to 325 F (160 C) for another 10 to 15 minutes or until the scones are golden brown. Don’t over bake or your scones will turn out too tough and crusty.
Take scones out of the oven and place on a wire rack to cool.
Enjoy and store: Eat warm, filled with jam, butter or cream.
These delicious sourdough scones are best eaten the day they are baked, but leftover scones keep well in an airtight container at room temperature for up to 2 days.