Pre-heat oven to 350F (180C). Lightly grease and flour or spray a 10-12 medium muffin tin or line with cupcake wrappers.
In a large bowl or stand mixer sift together the flour, cocoa, baking soda, baking powder and salt.
Add the sugar and whisk together, add the eggs, buttermilk, warm water, oil and vanilla beat on medium speed until smooth, approximately 2 minutes, batter will be thin.
Divide the batter between the muffin tin and bake for approximately 15-20 minutes or until toothpick comes out clean. Let cool, then remove from the tin.
FOR THE CHOCOLATE BUTTERCREAM FROSTING
In a large bowl, beat the butter on medium speed until creamy, approximately 2 minutes. Add the sifted powdered sugar and cocoa powder mix on low speed then increase to medium speed for about 1 minutes. Add the cream/milk, salt, and vanilla extract. Beat on low speed for 30 seconds, then increase to medium/high speed and beat for 1 minute. If the frosting is too thin then add 3-4 tablespoons of sifted powdered /icing sugar if too thick then add a tablespoon or more of cream/milk.
Notes
To make cake flour, for every cup of all-purpose flour, remove two tablespoons of flour and replace with two tablespoons of cornstarch, sift together to remove any lumps.To make sour milk – add 1/2 tablespoon of lemon juice or white vinegar to 1/2 cup / 120ml measure and top off with milk, let sit for about 10 – 15 minutes before using.Store leftover cupcakes at room temperature in an airtight container for up to 5 days. For longer storage up to a week, store in the refrigerator but bring to room temperature before serving. These basic chocolate cupcakes freeze best without frosting. Store unfrosted chocolate cupcakes in a freezer bag for up to 3 months. Thaw and then frost if desired and enjoy.