Preheat and Prep – Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream Butter and Sugars—In a large bowl, beat the softened butter, brown sugar, and granulated sugar until light and fluffy. See the Pro Tip above.
Add Wet Ingredients – Mix in the sourdough discard, whole egg, and vanilla extract until well combined.
Combine Dry Ingredients – Whisk together the flour, baking soda, cornstarch, and salt in a separate bowl.
Mix the Dough – Gradually add the dry ingredients to the wet ingredients, stirring until combined. Fold in the chocolate chips.
Scoop and Bake: Using a cookie scoop, scoop cookie dough balls onto the parchment-lined baking sheet, spacing them about 2 inches apart.
Bake – Bake for 10-12 minutes or until the crispy edges are golden brown.
Cool —Let the cookies cool on the cookie sheet for a few minutes before transferring them to a wire rack.