Preheat your oven to 350°F (175°C) and line your muffin tin with paper liners or grease it well to prevent sticking.
In a large mixing bowl, whisk together the all-purpose flour, light brown sugar, cocoa powder, instant espresso powder (if using), baking powder, baking soda, and a pinch of salt. Ensure all ingredients are well combined.
In another bowl, whisk together the buttermilk, eggs, canola oil, brewed coffee (if using), and vanilla extract until smooth and well mixed.
Make a well in the dry ingredients and pour in the wet mixture. Stir gently with a spatula until just combined. Be careful not to overmix; it’s okay if there are a few lumps.
Add the semi-sweet chocolate chips to the batter and fold them in gently until evenly distributed.
Scoop the batter into the prepared muffin tin, filling each cup about two-thirds full. This allows room for the muffins to rise beautifully.
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Once baked, remove the muffins from the oven and let them cool in the tin for about 5 minutes. Then transfer them to a wire rack to cool completely. Enjoy your Chocolate Lovers Chocolate Chocolate-Chip Muffins warm or at room temperature!