Preheat your oven to 425°F (220°C). Line every other muffin well of your muffin pan with paper liners (this allows for better air circulation and taller muffin tops). If you’re skipping liners, grease each muffin cup thoroughly with butter or nonstick spray to prevent sticking.

In a large mixing bowl, whisk the brown sugar, melted butter (cooled), maple syrup, and vanilla until the mixture looks glossy and well combined — about 1–2 minutes. This helps dissolve the sugar slightly for a smoother texture.

Add the eggs and whisk again for another minute, until the batter thickens slightly and looks creamy and cohesive.

Sift in or add the Dutch-process cocoa powder, whisking until no dry pockets remain. The mixture should look rich and dark, like brownie batter.

Switch to a spatula and gently stir in the mashed bananas, sour cream, baking powder, baking soda, and salt. Stir until everything is fully combined — this ensures even distribution of the leavening agents so your muffins rise evenly.

Sprinkle in the gluten-free flour blend, folding gently until just combined. The batter will be thick and slightly lumpy — avoid overmixing to keep your muffins tender.

Pour in the milk, then grab your whisk again and mix until the batter is smooth and uniform. Use your spatula to scrape down the sides and bottom of the bowl to make sure all ingredients are evenly incorporated.

Optional but recommended: Let the muffin batter rest for 20–30 minutes at room temperature before baking. This hydrates the gluten-free flour for a higher, domed muffin top. You can also refrigerate the batter overnight and bake in the morning — just let it sit at room temperature for 10–15 minutes before scooping.

Fold in ? cup (114 g) of chocolate chips, distributing them evenly throughout the batter so every muffin has chocolate in every bite.

Use a cookie scoop or large spoon to fill prepared muffin cups well about ¾ full. Fill every other cup to allow for more heat circulation, which helps them rise tall and bake evenly.

Lightly tap or jiggle the pan on the counter to help the batter settle and level out.

Sprinkle the reserved ? cup of chocolate chips evenly over the tops of the muffins for that bakery-style finish.

Bake in the center of the oven at 425°F (220°C) for 8 minutes, then reduce the oven temperature to 350°F (177°C) (without opening the door!) and bake for another 8–10 minutes, or until the tops are puffed, slightly cracked, and spring back when lightly pressed in the center.

Let the muffins cool in the pan for about 10 minutes, then use a butter knife to gently loosen the edges. Transfer to a wire rack to cool completely.

These muffins are delicious warm with melty chocolate, or at room temperature once the flavors have settled.