1. Preheat the oven to 350 degrees F and line a cupcake tin with cupcake liners. 

   Tip: To help prevent the cupcake liners from sticking to the cupcakes, spray the liners lightly with cooking spray before adding the batter. 
2. In a medium bowl, whisk together the flour, cocoa powder, espresso powder, baking powder, baking soda, and salt. Set to the side. 
   140 grams all-purpose flour, sifted, 40 grams unsweetened cocoa powder, 3 grams espresso powder, 4 grams baking powder, 3 grams baking soda, 1 gram salt
3. In a liquid measuring cup, whisk together the milk, sour cream, and sourdough discard until smooth. 
   60 grams milk, room temperature, 140 grams sour cream, room temperature, 140 grams sourdough discard, room tempearture
4. In a large mixing bowl, whisk together the melted butter and sugars.
   113 grams unsalted butter, melted, 100 grams white sugar, 110 grams light brown sugar
5. Next, add in the eggs and sourdough discard mixture, and mix until combined. Scrape the sides of the bowl when needed. Add vanilla extract and mix well. 
   2 large eggs, 4 grams vanilla extract
6. Finally, add the dry ingredients to the wet ingredients. Mix by hand with a spatula until all of the ingredients are just combined.

   Be careful to not over mix. This can lead to a dense cupcake.
7. LONG FERMENT: To long ferment, cover the just-mixed batter and place it into the fridge overnight. The following day, divide the batter evenly in the muffin pan and bake. You might need to add a few minutes to the bake time since the batter is chilled.
8. This recipe bakes about 16 cupcakes, so you will need to bake them in batches. Divide the batter evenly into 16 cupcake liners and fill about 3/4 of the way full. 
9. Bake the Sourdough Chocolate Espresso Cupcakes for 15-16 minutes. The cupcakes are done when a toothpick comes out clean. 
10. Remove the cupcakes from the oven. Keep the cupcakes in the cupcake tin for an additional 5 minutes, then place them on a wire rack to cool completely.

Espresso Buttercream Frosting

1. In a stand mixer with a whisk attachment, beat the room-temperature butter at medium speed for 2 minutes, or until light and fluffy.

   This can also be done with a hand mixer.
   226 grams unsalted butter, room temperature
2. Next, add the powdered sugar to the butter, one cup at a time at medium speed. 
   325 grams powdered sugar
3. Finally, add the cooled shot of espresso and salt. Mix until combined. 
   1 espresso shot, cooled, pinch of salt