Preheat and prep: Heat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease well. This higher starting temp helps create nice domed tops.

Whisk the dry ingredients: In a large bowl, whisk 1 3/4 cups all-purpose flour, 1/2 cup unsweetened cocoa powder, 3/4 cup granulated sugar, 1/4 cup packed light brown sugar, 2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon fine salt until no lumps remain.

Add optional flavor boost: If using, whisk in 1 teaspoon espresso powder. It won’t make the muffins taste like coffee—it just deepens the chocolate.

Mix the wet ingredients: In a separate bowl or large measuring cup, whisk 3/4 cup buttermilk, 1/2 cup neutral oil, 2 large eggs, and 2 teaspoons vanilla extract until smooth.

Combine wet and dry: Pour the wet mixture into the dry ingredients. Stir gently with a spatula until just combined. A few streaks of flour are okay. Avoid overmixing.

Fold in the chocolate: Add 3/4 cup semi-sweet chocolate chips and 1/2 cup mini chips or chopped dark chocolate. Fold lightly so the chips are evenly distributed.

Fill the muffin cups: Divide the batter among the cups, filling each about 3/4 full. For an extra treat, sprinkle a few more chips on top or add a pinch of coarse sugar for a slight crunch.

Start hot, then reduce: Bake at 400°F (200°C) for 5 minutes. Without opening the oven, reduce the temperature to 350°F (175°C) and bake for 12–15 more minutes, until a toothpick comes out with a few moist crumbs.

Cool and set: Let the muffins cool in the pan for 5 minutes, then move them to a wire rack. They’ll continue to set as they cool, keeping the centers soft.

Serve: Enjoy warm while the chips are melty. They’re also great at room temperature and even better the next day.