Preheat your oven to 350°F (175°C).

Line a 12-cup muffin tin with cupcake liners.

In a large bowl, use an electric mixer to beat the softened butter and granulated sugar until light and fluffy (about 2–3 minutes).

This step adds air to the batter, giving you fluffy cupcakes.

Beat in the eggs, one at a time, mixing well after each addition.

Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt.

Add half of the dry mixture to the butter mixture, then add the milk, and finish with the remaining dry ingredients.

Mix until just combined—don’t overmix!

In a small bowl, stir together the cocoa powder, milk, and sugar to create a smooth chocolate mixture.

Scoop out about 1/2 cup of the vanilla batter and mix it with the chocolate blend to create your swirl batter.

Add a spoonful of vanilla batter to each cupcake liner, then a small spoonful of chocolate batter on top.

Use a toothpick or skewer to gently swirl the two together—just a few turns will do the trick!

Bake for 18–20 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.