If you are using a stand mixer, use the beater (paddle) attachment on your mixer. (If you don't have a beater attachment or a stand mixer, it's okay. Just use the whisk attachment, or the attachments that came with your handheld mixer.)
Make sure your butter and cream cheese are softened. They should be a little cooler than room temperature. (The cream cheese can be a little colder than the butter.) Don't microwave them though.
Add the butter and cream cheese to a bowl and beat very well on medium to medium/high speed until creamy.
Scrape down the sides of the bowl and beat again until well mixed.
Add in the cocoa powder and mix well. Scrape down the sides of the bowl and mix again.
Add in three cups of confectioner’s sugar plus the salt and one tablespoon of milk or cream. Beat on low until incorporated and then medium until well mixed.
Add the last three cups of confectioner’s sugar and mix on medium until well incorporated.
Scrape down the sides of the bowl and mix again.
Add the optional red velvet flavoring and mix on medium high until well mixed. (If you don't have red velvet flavoring, or do not want to use it, just use a teaspoon of vanilla extract instead.)Scrape down the sides of the bowl and mix again.) Add in two teaspoons of the red gel food coloring and mix on medium to medium/high until well mixed. Add more food coloring if needed and scrape down the sides of the bowl, then mix again. Do this until you reach the desired color.
Now, check the consistency. If it’s too thick, add another tablespoon of milk and mix again on medium. If it's too thin, add in another cup of confectioners sugar. Adjust the coloring if needed.
Fold in the mini chocolate chips.
Spread or pipe onto cupcakes. (If you want to pipe onto cupcakes, pop the buttercream into the fridge for it to firm up a bit and use a large opening piping tip like an 8B.)