Preheat oven to 325 degrees Fahrenheit (160 degrees Celsius).

Whisk the flour, cocoa, baking soda, espresso powder, if using, salt, and

cinnamon in a large mixing bowl. Stir in the chocolate chips.

Whisk the remaining ingredients well in a separate bowl. Make a well in the center of the dry ingredients and add the wet ingredients. Stir gently just until incorporated.

Fill the muffin cups two-thirds of the way with the batter. If you’d like, you can sprinkle some more chocolate chips on top.

Bake for 18–22 minutes, or until a toothpick comes out clear.

Place the pan on a wire rack. Let the muffins cool in the pan for five minutes, then gently transfer them to the cooling rack so they don’t get soggy.