Preheat oven to 180°C (conventional). Line a 12-cup muffin pan with paper liners.
Blend oats in a small food processor until finely ground to make oat flour, or use store-bought.
Mash bananas in a large bowl until smooth - a fork or clean hands both work well.
Add the remaining wet ingredients - maple syrup, melted coconut oil, vanilla, vinegar and eggs.
Stir in the dry ingredients - oat flour, almond flour, baking powder, baking soda and salt mix until just combined. Avoid overmixing.
Fold in the blackberries, halving any that are large. Reserve a few (or use extra) to top before baking, if desired.
Let the batter rest for 5-10 minutes.
Scoop the batter into the prepared muffin tin, filling each cup about 2/3 full. This recipe makes approximately 10 muffins.
Top with optional cinnamon sugar (1 tbsp unrefined coconut sugar + 1/4 tsp cinnamon). It adds a lovely hint of warm spice that pairs beautifully with the muffins! Highly recommended. Finish with a few reserved blackberries, halved if necessary.
Bake at 180°C (conventional) for 23 minutes, or until the tops are golden brown and a toothpick comes out clean. Allow to cool in the pan for 5-10 minutes.