Preheat Oven and Prep Pan:
Heat oven to 425°F (220°C). Prepare a 12-cup muffin tin by inserting liners or coating with nonstick spray.Whisk Dry Ingredients:
In a large mixing bowl, combine 2 cups (250g) flour, cocoa powder, baking powder, baking soda, and salt; whisk until uniform.Mix Wet and Dry:
In another medium bowl, beat eggs, buttermilk, sugar, oil, and vanilla until homogeneous. Add wet mixture to dry ingredients along with melted chocolate; fold gently until just incorporated—do not overmix. Batter will be thick.Coat and Fold Chips:
In a small bowl, mix 3/4 cup (128g) chocolate chips with 1 teaspoon (3g) flour to prevent sinking. Gently fold coated chips into batter.Fill Muffin Cups:
Spoon batter evenly into prepared cups, filling nearly to the rim. Top with remaining 1/4 cup (42g) chocolate chips.Bake at Two Temperatures:
Bake at 425°F (220°C) for 5 minutes. Without removing from oven, lower temperature to 350°F (175°C) and bake another 15–17 minutes until a toothpick inserted in center emerges clean.Cool Muffins:
Let muffins cool in pan for 5 minutes, then transfer to a wire rack to cool fully before serving.