Preheat oven to 425°F. Line muffin tins with paper liners.
Whisk flour, cocoa, baking soda, baking powder, and salt in a bowl.
Mix espresso, vanilla, sugar, eggs, and buttermilk in a second bowl. Stream in melted butter.
Add dry mixture to wet and stir until just combined.
Fold in most of the chocolate chips, reserving some for tops.
Scoop batter into muffin cups, filling to the top.
Bake 5 minutes at 425°F, then reduce to 350°F and bake 10–12 minutes more.
Place reserved chocolate chips on hot muffins.
Cool slightly, then dust with confectioner’s sugar if desired.