Step 1: Preheat and Prepare

Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or lightly grease with nonstick spray.

Step 2: Prepare the Dry Ingredients

In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, salt, and cinnamon. Stir until well combined to evenly distribute the dry ingredients.

Step 3: Mix the Wet Ingredients

In a separate bowl, whisk the milk, vegetable oil, eggs, brewed espresso, and vanilla extract until smooth and fully incorporated.

Step 4: Combine Wet and Dry Ingredients

Gradually add the wet mixture into the dry ingredients, stirring gently with a spatula or wooden spoon. Mix until just combined—do not overmix, as this can result in dense muffins.

Step 5: Fold in the Chocolate

Gently fold in the chocolate chips and chopped chocolate pieces, ensuring they are evenly distributed throughout the batter.

Step 6: Fill the Muffin Cups

Using a spoon or ice cream scoop, divide the batter evenly among the 12 muffin cups, filling each about ¾ full.

Step 7: Bake to Perfection

Place the muffin tin in the preheated oven and bake for 18-22 minutes, or until a toothpick inserted into the center comes out with only a few moist crumbs.

Step 8: Cool and Enjoy

Remove the muffins from the oven and let them cool in the pan for 5 minutes before transferring them to a wire rack. Enjoy warm or at room temperature!