Preheat oven to 350. Spray a 12 cup muffin tin with cooking spray or line with cupcake liners.
In a heat-safe bowl, place the butter and 1/2 cup of chocolate chips. Microwave for about 45 seconds until butter is melted and chocolate chips are nearly melted. Stir butter and melted chocolate together until well-combined.
Place bananas in a large bowl and mash with a fork or potato masher.
To the mashed bananas, add chocolate/butter mixture, sugar, eggs, and vanilla. Mix well with a wooden spoon until well-combined.
Add dry ingredients: flour, salt, baking soda, and the remaining chocolate chips. Mix well until dry ingredients are completely incorporated.
Spoon batter into muffin tin (or liners) until about 3/4 full.
Top each muffin with 5-6 more chocolate chips.
Bake 20-22 minutes until a toothpick inserted into the middle of a muffin comes out clean or muffins spring back when lightly touched.
Sprinkle tops lightly with sea salt.