Cream Butter and Sugar: Add room temperature butter and sugar into a large bowl and cream together using beaters until the mixture is light and fluffy.
Add Wet Ingredients: Add egg, sourdough discard, and vanilla extract, and mix until combined.
Add Dry Ingredients: Add baking soda, salt, and flour on low speed.
Fold in Sprinkles: Fold in ½ cup of sprinkles to the dough.
Scoop Dough: Scoop the cookie dough into balls using a 1 ½ Tablespoon cookie scoop. This will make 36 cookies.
Dip in Sprinkles (optional): Add ¼ cup sprinkles to a small bowl and dip the top of the dough balls in the sprinkles.
Refrigerate Dough: Add the dough balls to a lined baking sheet. Refrigerate covered for at least 30 minutes or up to 2 days.
Bake: Preheat the oven to 350°F. Divide the dough balls between 2 lined large baking sheets. Bake for 12-15 minutes or until the edges are just slightly turning golden brown and the middle of the cookie has lost its sheen.
