Preheat oven to 400 degrees and line a muffin tin with baking papers or spray with nonstick cooking spray.
In a stand mixer or with an electric hand mixer, beat together butter and sugar until creamy.
Add in eggs and sour cream, mix well.
In a small bowl, peel and mash the over ripe bananas until they are almost a liquid.
To the mixing bowl, add the bananas, flour and baking soda. Mix until well combined, there may still be lumps, that is ok.
Optional: stir in mini chocolate chips keeping 2 tablespoon set aside to sprinkle on tops of muffins before baking.
Using a large spoon, scoop batter into prepared muffin cups until nearly full. Sprinkle tops with optional leftover mini chocolate chips
Bake muffins for 10 minutes at 400 then, without opening the oven door, reduce oven temp to 350 and continue baking for another 6-8 minutes. Test a muffin with a toothpick to make sure it comes out clean. If there is still batter on the toothpick, continue baking the muffins for 2 minutes more and re-checking.
Let muffins cool and enjoy!
Store in an airtight container or ziplock bag at room temperature for up to 4 days.
Baked muffins can be cooled and frozen for up to 4 months.