01 - Set oven to 375°F. Line two baking sheets with parchment or silicone mats.
02 - Combine flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl; whisk to blend.
03 - Whisk melted butter with granulated and brown sugars until smooth. Add eggs one at a time, fully incorporating each. Stir in vanilla extract.
04 - Add half the dry mixture to wet ingredients; mix gently. Pour in buttermilk, then add remaining dry ingredients. Stir until just combined without overmixing.
05 - Fold semisweet chocolate chips evenly into the batter.
06 - Drop batter by 1/4 cupfuls or with a large scoop onto prepared sheets, spacing approximately 2 inches apart.
07 - Bake for 10 to 12 minutes until edges are set and centers appear just baked; avoid overbaking.
08 - Cool muffin tops on the pan for 5 minutes, then transfer to a wire rack to cool completely.