Preheat your oven to 425°F (220°C) and line every other muffin well with paper liners in a 12-cup muffin pan.

In a medium saucepan over medium heat, melt the salted butter until golden brown and nutty in aroma, about 5-7 minutes.

In a large mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, espresso powder, and salt.

In another bowl, whisk together the cooled browned butter and granulated sugar until well combined, then add eggs, buttermilk, Greek yogurt, and vanilla extract.

Gradually fold the dry ingredients into the wet mixture with a rubber spatula until just combined.

Gently fold in both mini and regular chocolate chips.

Overfill each muffin liner with 6-8 tablespoons of batter.

Place the muffin pan in the oven and bake at 425°F (220°C) for 7 minutes, then reduce to 350°F (175°C) and continue baking for 12-15 minutes.

Let the muffins cool in the pan for 5-10 minutes before transferring them to a wire rack.