Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt until well combined.
In a large bowl, cream the softened butter, granulated sugar, and brown sugar together with an electric mixer on medium speed until light and fluffy, about 2-3 minutes.
Add the eggs one at a time to the butter mixture, beating well after each addition. Then, mix in the vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix on low speed until just combined, being careful not to overmix.
Divide the batter evenly among the prepared muffin cups, filling each about 2/3 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.