Heat oven to 350℉/177℃.
Line muffin tins with baking papers, or spray with baking spray. Set aside.
In a medium bowl, whisk together flour, cocoa powder, cocoa mix, baking powder, baking soda, and salt. Set aside.
With an electric mixer, beat butter and sugar until light and fluffy, 2-3 minutes.
Add eggs, one at a time, beating well after each addition.
Stir in vanilla.
Mix in dry ingredients alternately with milk, beginning and ending with the dry ingredients.
Use a 3 Tablespoon scoop to portion batter into prepared muffin tins.
Bake for 15-20 minutes, or until done.