Preheat the oven to 220°C. We need the oven to be nice and hot when we pop the muffins in to give them that fluffy, signature muffin top. Line a muffin pan with 16 paper liners and set aside.

In a medium bowl, whisk together flour, sugar, baking powder, baking soda, and salt. Set aside.

In a separate bowl, whisk warm water (this helps activate the cocoa powder and gives you a more intense chocolate flavor) with cocoa powder, and 2 tsp instant espresso or coffee (optional) together until smooth.

Then mix in buttermilk, oil, melted and cooled butter, 2 large eggs, and 1 tsp of vanilla extract into the cocoa mixture until combined.

Pour the dry ingredients into the wet ingredients and mix until just combined and you no longer see streaks of flour. The batter should not be all the way smooth, and it's ok if there are still some small chunks in it.

Then fold chocolate chips into the batter until they're evenly distributed. If desired, add a sprinkle of coarse sugar and a few extra pieces of chocolate on the top of each muffin.

for gluten free dough: let dough rest for 30 min

Bake one tray at a time. Bake the muffins for 3 minutes at 220°C to give them a nice rise and a domed top, then (keeping the muffins in the oven) reduce the oven temperature to 175°C. Continue to bake for an additional 12-14 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs (but don't get confused by any melted chocolate chips!). Then remove them from the oven.

Let the muffins cool in the pan for 10 minutes, then move them to a wire rack to finish cooling.