Preheat oven to 350°F. Line 12-count cupcake tins with 20 cupcake liners.
In a medium bowl, whisk the flour, unsweetened cocoa powder, baking powder, baking soda, and salt together. Set aside.
1½ cups all-purpose flour, ¼ cup unsweetened cocoa powder, 1 teaspoon baking powder, ½ teaspoon baking soda, ¼ teaspoon kosher salt
Place butter and chocolate chips in a large microwave-safe bowl. Heat in microwave (on high) for 1 minute, then stir well. If not fully melted, continue to heat and stir well in 30-second intervals until melted. This should be melted but not very hot.
1 cup unsalted butter, 1 cup semisweet chocolate chips
Stir (with a mixing spoon, not electric beaters) the brown sugar into the melted chocolate mixture.
1 cup brown sugar
Whisk the eggs and vanilla into the melted chocolate mixture.
2 large eggs, 1 teaspoon pure vanilla extract
Pour half of the dry ingredients into the wet ingredients and stir just until combined. Do not overmix.
Stir all the buttermilk into the wet mixture. Stir just until mixed.
½ cup buttermilk
Pour the remaining half of the dry ingredients into the wet ingredients and stir just until mixed and no white flour remains. Don’t overmix or the cupcakes won’t bake into the correct soft texture.
Fill the cupcake liners halfway full with cupcake batter. This will be 20 cupcakes. Don’t overfill cupcake liners or the cupcakes won’t rise properly.
Place cupcakes into the oven and bake for 15-16 minutes, or until a toothpick inserted in the middle comes out clean.
Remove the cupcakes from the hot cupcake tins and place them on a wire rack to cool completely before frosting. It’s important to remove the cupcakes from the hot cupcake tin as soon as they come out of the oven so they don’t continue baking and dry out.