Preheat oven to 350°. Place paper liners in all wells of one 12-cup and one 6-cup cupcake tin.
Whisk flour, cocoa powder, baking soda and salt together in a small bowl to aerate and combine; set aside.
In a large bowl, using an electric mixer set on medium-high speed, beat butter until creamy (for about two minutes).
Adding sugar gradually, beat until light and fluffy (for about three minutes). Scrape down the bowl once or twice.
Beat in vanilla extract. Beat in eggs one at a time, scraping down after each addition. Allow each egg to be absorbed before continuing.
Add the flour mixture in four additions, alternating with milk. Begin and end with the flour mixture. After each addition, beat briefly until smooth on low-medium speed.
Divide batter evenly among cupcake wells. Bake for about 22 minutes or until a toothpick inserted in the center shows a few moist crumbs.
Cool pans on racks for five minutes, then remove cupcakes to cooling racks to cool completely.