Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners.
In a large mixing bowl, whisk together the flour, cocoa powder, granulated sugar, brown sugar, baking powder, baking soda, and salt.
In another bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Fold in the semi-sweet chocolate chips, white chocolate chips, and milk chocolate chips.
Divide the batter evenly among the muffin cups, filling each about ¾ full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.