Preheat the oven to 350°F (177°C). Line your cupcake tin with 12 cupcake liners. Set aside.
In a large mixing bowl, whisk the all-purpose flour, cocoa powder, espresso powder, baking powder, baking soda, and salt. Set aside.
In a medium bowl, whisk together the sourdough discard, eggs, white sugar, brown sugar, oil, vanilla extract, and milk.
Pour the wet ingredients mixture into the dry ingredients. Stir until combined. Remember not to overmix the ingredients! The batter will be slightly thin.
Fill the liners halfway with the batter. Each should be only halfway full. Bake for 18-20 minutes or until done. You will know when the cupcakes are done baking when a toothpick inserted into the center of the cupcake comes out clean.
Place the cupcakes on a wire cooling rack. Let cool completely before frosting.
Espresso Powder: Espresso powder will not make the cupcakes taste like coffee. Instead, it will deepen the chocolate flavor. If coffee is not your thing, you can omit the espresso powder.
Cocoa Powder: Use natural cocoa powder. Do not use Dutch-processed cocoa powder.
Storing Instructions: Unfrosted cupcakes can be stored at room temperature for up to three days. Frosted cupcakes should be stored in the fridge. Frosted and unfrosted cupcakes can be frozen for up to two months. To defrost, store in the refrigerator overnight.
Sourdough Cake: You can turn this into a cake. However, I recommend making my Sourdough Chocolate Cake recipe instead. It's very moist and rich.