Adjust oven rack to middle position and preheat oven to 350°F. Line muffin tin with paper liners.
In a large bowl, whisk together flour, cocoa, baking soda, salt, sugar, and instant espresso powder until combined. Stir in coffee, vanilla, and vinegar until batter is formed. Stir in chocolate chips or chunks. Fill each muffin tin 3/4 way full with batter. Bake until a cake tester inserted into the middle of a muffin comes out clean, about 18 minutes. Transfer muffins to a wire rack to finish cooling.
Deepstash helps you become inspired, wiser and productive, through bite-sized ideas from the best articles, books and videos out there.