Preheat the oven: Preheat the oven to 425°F. Line a 12-cup muffin tin with paper liners or lightly coat with nonstick cooking spray.
Combine the dry ingredients: In a medium bowl, whisk together the almond flour, cake flour, ground flaxseed, baking soda, baking powder, cinnamon, and salt until evenly combined.
2 1/4 cups almond flour, 3/4 cup cake flour, spooned and leveled, 2 Tbsp. ground flaxseed, 1 tsp. baking soda, 1/2 tsp. baking powder, 3/4 tsp. cinnamon, 1/2 tsp. kosher salt
Mix the wet ingredients: In a large bowl, whisk together the mashed bananas, eggs, Greek yogurt (or sour cream), melted coconut oil, brown sugar (if using), and vanilla extract until smooth.
3 small over ripe bananas, 3 large eggs, room temperature , 1/3 cup full-fat Greek yogurt, 2 Tbsp. melted coconut oil, 2-4 Tbsp. light brown sugar, 2 tsp. vanilla extract
Combine the batter: Add the dry ingredients to the wet ingredients and gently fold together with a rubber spatula just until only a few streaks of flour remain.
Add chocolate chips: Fold in the chocolate chips, being careful not to overmix. The batter will be thick.
1 cup dark chocolate chips
Fill the muffin cups: Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full. Sprinkle a few extra chocolate chips (and coarse turbinado sugar, if desired) over the tops.
Bake: Bake at 425°F for 5-6 minutes Start Timer. Without opening the oven door, reduce the oven temperature to 350°F and continue baking for 10-12 minutes Start Timer, or until the tops are golden and a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Cool: Let the muffins cool in the pan for 5 minutes Start Timer, then transfer them to a wire rack to cool completely. ENJOY!