Preheat oven to 425°F with a rack placed in the middle or upper third of the oven. Prepare a muffin pan by lining it with cupcake liners.
Whisk the flour, salt, baking powder, and baking soda in a small bowl. Sift in the cocoa powder and mix well. Set aside.
In a separate bowl, cream the sugar and butter. This can be done with a handheld mixer or stand mixer. Mix in the eggs, blend thoroughly, then mix in the mashed banana.
Melt 1/3 cup chocolate chips in a microwave or double boiler. If using a microwave, melt the chocolate in 20-second bursts, stirring between. It usually takes about 3 bursts in my microwave.
Add dry ingredients and buttermilk to the batter in alternating batches until just incorporated. Try to end with the dry ingredient addition, and be sure not to over mix. Slowly stir in melted chocolate. Fold in half of the remaining chocolate chips.
Distribute the batter into the muffin tin, filling nearly to the top. Top with remaining chocolate chips.
Bake the muffins for 9 minutes, then lower the oven temperature to 350°F (do not open the oven door) and continue baking for another 7 to 8 minutes, or until the muffins are domed and the tops are firm when gently pressed. A toothpick inserted into the center of the muffins should come out clean.
Chocolate Banana Muffins Tips/FAQs
How ripe should the bananas be? VERY ripe -- dark and spotted, soft and fragrant bananas are what you are looking for and will make these muffins sweet and moist.
Why do you bake it at two temperatures? I start the baking process at high heat to encourage as much lift and to get nice domes on the muffins. If looks aren't important to you and you don't feel like watching the clock, you can bake the muffins at 350°F for 18-20 minutes. The tops might be a little flatter, but they will still taste wonderful!
How should I store the muffins? First, cool the muffins completely. Place the muffins in an airtight container lined with a paper towel. Keeping the muffins airtight will help prevent them from drying out, and the paper towel will absorb any excess moisture.