Preheat the oven to 375 F. Butter 12 muffin cups or line them with paper liners.
In a large bowl, sift together flour and cocoa powder. Add baking powder, baking soda, salt, and sugars and mix to combine.
Beat together the eggs, buttermilk, coffee, melted butter, espresso powder, and vanilla extract using a mixer on low speed.
Pour the wet ingredients into the flour mixture then fold with a wooden spoon or rubber spatula until well combined. Don't overmix. The batter should be thick and lumpy.
Gently fold in the chocolate chips.
In a small bowl, mix together the brown sugar, chopped pecans, and mini chocolate chips to make the topping.
Divide the muffin batter evenly between the muffin cups, then sprinkle the topping evenly on top of the batter with a spoon.
Bake for 15-18 minutes, or until a toothpick inserted into the center of the muffins comes out clean.
Transfer the muffins to a wire rack and let cool for 10 minutes before serving.