Sourdough Chocolate Cupcakes

Preheat your oven to 350F and prepare your cupcake pan with liners. If you want to ferment your batter, see the notes below for the instructions you'll need a day in advance.
In a large mixing bowl, mix your dry ingredients together. Set aside.
¾ cup all-purpose flour, ½ cup cocoa powder, 1 teaspoon baking powder, ¾ teaspoon baking soda, ¼ teaspoon salt
In a medium bowl, mix together your wet ingredients. Slowly mix your wet ingredients into your bowl of dry ingredients until just combined. The batter will be thin; Do not over mix!
2 eggs, ⅓ cup sourdough discard, ½ cup cane sugar, ½ cup brown sugar, ⅓ cup vegetable oil, 2 teaspoons of vanilla extract, ½ cup milk
Use a three-tablespoon cookie scoop to evenly divide the batter between 14 cupcake liners. If you don't have a scoop like this, aim for ½-3/4 full in the liners.
If you only have a 12-cupcake pan, it is fine to set the remaining batter aside while the first 12 bake.
Bake the cupcakes for 18-20 minutes at 350F until a toothpick inserted in the center comes out clean. 18 minutes is perfect for me, typically. Allow to cool completely before decorating.

With a stand mixer and paddle attachment (or mixing bowl with a handheld mixer), beat the softened butter and vanilla until smooth and creamy. Scrape the sides of the bowl.
In a medium bowl, whisk together cocoa powder and powdered sugar. Slowly add the sugar mixture to the butter (if the sugar or cocoa is clumpy, use a sifter to add it in to ensure a smooth result). Slowly add in the 3 tablespoons of milk until you achieve your desired consistency.
1 cup salted butter, 3 ½ cups powdered sugar, 3 tablespoons milk, 2 teaspoons vanilla extract
Decorate your cooled cupcakes with the chocolate buttercream using a piping bag and icing tip (I used a Wilton 1M star tip) or even just a spoon or knife. Top with chocolate shavings* and/or sprinkles.