Preheat the oven to 350°F/175°C. Line a muffin pan with 12 liners or make your own.
In a large bowl, mash the bananas with a fork or potato masher. Whisk in the light brown sugar, vanilla extract, melted butter and sour cream.
In another bowl, whisk the flour with the oats, baking soda, baking powder, salt, cinnamon and nutmeg.
Pour the wet ingredients into the dry, stirring until just combined.
Keep a handful of chocolate chips to the side. Fold the rest of them into the batter.
Fill the liners to the top with the batter. Add the extra chocolate chips to the top of each muffin.
Bake in the oven for 25-30 minutes.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients about an hour or two before you start baking. Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt. Please note, I'm using Diamond Crystal Kosher Salt which is not as salty as Morton Salt. Morton Salt is way saltier! Storage: keep in an airtight container at room temperature for 2 days, or in the fridge for 4 days. Freezing: freeze baked and cooled muffins in a freezer bag for up to 2 months. Let them thaw in the fridge or at room temperature.