Preheat your oven to 400°F (200°C). Line a muffin tray with muffin liners, and I recommend lining every alternate cup.
In a large bowl, whisk together the milk, yogurt, light brown sugar, cane sugar, mashed banana, vegetable oil, and vanilla extract until smooth and combined.
In another bowl, combine, sift and mix the flour, baking powder, baking soda, salt, and cocoa powder.
Gradually add the dry ingredients to the wet ingredients and stir until just combined. Be careful not to overmix.
Fold in the chocolate chips, saving some for topping.
Cover and let the muffin batter rest for 30 minutes at room temperature.
Spoon the batter evenly into the muffin liners up to the rim.
Bake at 400°F (200°C) for 7 minutes. Then, reduce the temperature to 350°F (175°C) and bake for another 8–10 minutes, or until the muffins are firm to the touch and a toothpick inserted into the center comes out clean. Baking time may vary depending on the size of your muffins.
Top each muffin with the chocolate chunks or remaining chocolate chips.
Let the muffins cool on a wire rack for 10–15 minutes before enjoying. Enjoy your warm, gooey double chocolate banana muffins!
Store any leftovers in an airtight container at room temperature for 2–3 days.