1. 1. Cream the Butter and Sugar: In a large mixing bowl, using an electric mixer, beat the softened unsalted butter and granulated sugar together until the mixture is light and fluffy. This usually takes about 2-3 minutes. The mixture should look pale yellow and airy, indicating that enough air has been incorporated.

2. 2. Add Wet Ingredients: Beat in the large egg and vanilla extract until well combined. Then, add the sourdough discard and mix until just incorporated. The mixture might look a little curdled at this stage, but don’t worry, it will come together once the dry ingredients are added.

3. 3. Combine Dry Ingredients: In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Make sure these are thoroughly mixed to ensure even leavening throughout the cookies.

4. 4. Gradually Add Dry to Wet: Slowly add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough, as this can lead to tough cookies. Stop mixing as soon as no streaks of flour are visible.

5. 5. Fold in Sprinkles and Chill: Gently fold in the 1/2 cup of sprinkles by hand using a spatula. Once the sprinkles are evenly distributed, cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes. This chilling step helps firm up the dough, making it easier to handle and preventing the cookies from spreading too much during baking.

6. 6. Preheat and Prepare Baking Sheets: While the dough is chilling, preheat your oven to 375 F (190 C). Line two baking sheets with parchment paper or silicone baking mats. Pour some extra granulated sugar into a shallow bowl for rolling the cookies.

7. 7. Scoop and Roll Cookies: Remove the chilled dough from the refrigerator. Scoop out rounded tablespoons of dough and roll them into smooth balls between your palms. Roll each dough ball in the extra granulated sugar, ensuring it’s evenly coated. Place the sugar-coated dough balls about 2 inches apart on the prepared baking sheets.

8. 8. Bake Until Golden: Bake for 8-10 minutes, or until the edges are lightly golden and the centers are set but still look soft. The cookies might look slightly underdone in the middle, but they will continue to set as they cool. Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.