Prep: Preheat the oven to 350 F. Line 3 baking sheets with parchment paper.
Make the dough: Combine the butter and sugar in a large bowl. Mix until no lumps remain.
226 grams unsalted butter, 250 grams cane sugar
Add the egg yolks one at a time. Stir in the sourdough discard and vanilla until fully incorporated.
2 egg yolks, 75 grams sourdough discard, 1 teaspoon vanilla extract
Fold the dry ingredients in until no traces of flour remain.
300 grams all-purpose flour, 10 grams baking powder, 6 grams salt
Portion out the dough: Divide the dough into 18 large even portions (about 3 tablespoons each).
Roll the dough in cane sugar and arrange them on your prepared baking sheet.
100 grams cane sugar
Arrange 6 portions of dough on each baking sheet, ensuring they are evenly spaced. Avoid overcrowding the cookies.
Bake: Bake for 12 to 14 minutes or until the edges begin to brown.
Bake on the middle rack and only 1 sheet at a time. Chill the other baking sheets while you wait.
Cool: Let the cookies cool and set completely on the hot baking sheet for 5 minutes before moving them to a wire rack.
Serve: These cookies taste best at room temperature and even better the day after they are baked.
Store: Store in an airtight container at room temperature for up to 5 days.