1. Preheat the oven to 350°F (175°C) and position the oven rack in the center. Generously grease a 12-cup muffin pan. Do not use paper liners; they'll stick.

2. Blend the oats in a blender until they form a fine oat flour. Transfer the oat flour to a large mixing bowl.

3. Measure 1 cup of mashed ripe bananas. If you have extra, slice thinly for topping. To the oat flour bowl, add the sugar (if using), baking powder, baking soda, cinnamon, and cornstarch. Whisk the dry ingredients thoroughly to combine.

4. In the blender jar, combine the cottage cheese, 1 cup of mashed banana, eggs, and vanilla. Blend on medium-high speed for 30 seconds, until the mixture is smooth and no cottage cheese curds are visible.

5. Pour the blended wet mixture over the dry ingredients in the large bowl. Stir gently with a rubber spatula until just combined, being careful not to overmix. A few lumps are fine.

6. Let the batter sit in the bowl for 5 minutes to allow the oats to absorb moisture and thicken. Then, spoon it into the muffin cups, filling each about ¾ of the way to the top. If using, arrange banana slices on top now.

7. Bake for 25 to 28 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.

8. Turn the oven off, crack the door open, and let the muffins sit inside for 5 minutes. This helps prevent sinking. Remove from the oven and cool in the pan for another 5-10 minutes before carefully removing them to a wire rack to cool completely.