Preheat the oven to 350°F (175°C) and line three baking sheets with parchment paper. Chill sheets in the fridge if you have them.

Combine 226 g cold-but-softened butter and 250 g cane sugar in a large bowl. Beat until smooth and no lumps remain — about 2–3 minutes by hand or 1–2 minutes with a mixer.

Add the 2 egg yolks one at a time, mixing until incorporated. Stir in 75 g sourdough discard and 1 teaspoon vanilla extract until uniform.

Whisk together 300 g all-purpose flour, 10 g baking powder, and 6 g salt. Fold the dry ingredients into the wet mixture until no traces of flour remain.

Divide the dough into 18 large portions (about 3 tablespoons each) using a cookie scoop.

Roll each portion in the 100 g cane sugar until evenly coated. Arrange 6 portions on each parchment-lined baking sheet, spacing them evenly.

Bake one sheet at a time on the middle rack for 12 to 14 minutes, or until edges begin to brown and centers look set.

Let cookies cool on the hot baking sheet for 5 minutes before transferring to a wire rack.