Chocolate Banana Muffins

Ingredients

• 3/4 cup dark brown sugar
• 6 tbsp unsalted butter, melted
• 1 large egg
• 1 tsp vanilla extract
• 3 large ripe bananas about 1 cup when mashed
• 1 cup all purpose flour
• 1/2 cup unsweetened cocoa powder
• 1 tsp baking powder
• 1 tsp baking soda
• 1/2 tsp salt
• 3/4 cup semi-sweet chocolate chips plus more for topping