Preheat oven to 350° F. Line muffin tin with 12 cupcake liners.
Place sugar, flour, baking soda, salt, and cocoa powder in small bowl. Stir until combined. Set aside.
Whisk egg, buttermilk, vanilla, vinegar, and oil together in medium bowl. Set aside.
Place chocolate chips in small bowl. Bring one cup of water to boil and pour 3 fl. oz. over chocolate chips. Stir to combine. Pour into egg mixture and whisk until combined.
Pour wet mixture into dry mixture and stir until combined.
Fill muffin cups using ¼ cup measuring cup.
Bake for 20-24 minutes or until tops bounce back slightly.
Peanut Butter Frosting
Place butter and peanut butter in bowl of stand mixer and combine on medium high speed for 1 minute.
Add confectioner’s sugar. Cover and combine on medium high speed until mixture is even consistency.
Add vanilla extract, heavy cream, and salt. Combine on medium high until mixture is even consistency.
For the drizzle, combine ½ cup chocolate chips or chunks and 1 Tbsp. coconut oil. Heat in microwave for up to 2 minutes at 50% power stirring every 30 seconds until melted. Place cupcakes on baking tray and drizzle melted chocolate by waving spoon above cupcake.
To achieve the amount of peanut butter frosting seen in the photos, double the frosting recipe.