Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them with butter and lightly dusting with flour.
In a large mixing bowl, combine the softened butter, granulated sugar, and brown sugar. Beat on medium speed until light and fluffy, about 3-5 minutes.
Add the eggs one at a time, mixing well after each addition. Then add the vanilla extract and mix until well blended.
In a separate bowl, sift together the all-purpose flour, cocoa powder, baking powder, baking soda, and sea salt.
Gradually incorporate the dry mixture into the wet mixture, alternating with the buttermilk. Start and finish with the dry ingredients, mixing on low speed until just combined.
Gently fold in the semi-sweet, dark, and milk chocolate chips until evenly distributed.
Divide the batter equally between the prepared cake pans, smoothing the tops.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.
Once cooled, frost with your favorite chocolate frosting or dust with powdered sugar.
Notes
For an eye-catching finish, garnish with chocolate shavings and fresh berries.