Preheat the oven to 425°F/220°C. Line a muffin pan with 12 liners. This recipe makes 14 muffins so you will have to bake them in two batches (unless you have a second muffin pan)
Blend the oats in a blender or food processor until it becomes a fine flour.
Whisk together the flour, oat flour, baking powder, baking soda, salt, cinnamon and nutmeg in a medium bowl or jug.
Use a potato masher or fork to mash the bananas
In the bowl of a stand mixer fitted with the paddle attachment, add the bananas, sugar, butter, eggs, vanilla, peanut butter and milk then beat on medium speed
Pour the dry ingredients into the wet and beat until combined
Keep a handful of chocolate chunks to the side. Fold the rest of them into the batter.
Fill the liners to the top with the batter. Sprinkle over the coarse sugar and add a few chocolate chunks to the top of each muffin
Bake for 5 minutes. Then, without opening the door, reduce the oven temperature to 350°F/175°C and bake for an extra 16-18 minutes.
Allow them to cool completely.
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 have provided a conversion to US cups but please note that I haven't tested the recipe with this method. Just click on 'US Customary' above ingredients. I make sure that all of my ingredients are at room temperature (except for the eggs!) before I start the recipe, so pull out all of the ingredients about 2 hours before you start baking. Chocolate Chips: You can substitute an equal amount of chips instead of chopping chocolate.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.Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your finished bake much creamier and richer.Storage: keep in an airtight container at room temperature for 2 days, or in the fridge for five days. Freezing: freeze baked and cooled muffins in a freezer bag. Let them thaw in the fridge or at room temperature.