Combine sugar and butter and cream until light and fluffy - about 3 minutes.
6 tbsp unsalted butter, softened to room temperature, ½ cup sugar
Add egg and mix on medium low until well combined - about 1 minute.
1 large egg, room temperature
Mash bananas until they are an applesauce consistency, and add to mixture. Mix on medium low until combined.
1 large ripe banana, very spotted
Add créme frîache and vanilla, and mix on medium low until combined.
2 tbsp créme frîache or full fat sour cream, 1 tsp vanilla extract
In a separate bowl combine all purpose flour, oat flour, baking soda, fine sea salt and ground cinnamon. Whisk well to disperse. Add to batter.
¾ cup all purpose flour, ½ cup oat flour, ½ tsp baking soda, ½ tsp fine sea salt, ¼ tsp ground cinnamon
Add chopped pecans to batter.
½ cup chopped pecans
Mix in flour and pecans until just combined. Stop mixing once you longer see any flour streaks - do not over mix.
Prepare muffin pan with liners. Scoop in batter to about ¾ of the way full.
Remove crumble from freezer and break apart with your hands. Generously top the muffins until consumed.
Bake at 350 F for 25 minutes, or until a toothpick comes out clean. Place on wire rack to cool.