Preheatthe oven to 350°F and position the oven rack in the center. Grease a 12-cup muffin pan well. Do not use paper liners; they'll stick.
Blend the oats in the blender to make 2 cups of oat flour. Sometimes you need to add an extra tablespoon of oats since it's not exactly 1:1. Add the oat flour to a large bowl.
Fill a 1-cup measuring cup with enough banana to fill the cup. If your bananas are on the larger side, save the remaining banana and slice it to top the muffins (like in the photo).
Make the batter:
To the oat flour bowl, add the sugar (if using), baking powder, baking soda, cinnamon, and cornstarch*. Whisk the dry ingredients to combine.
To a blender jar, add the cottage cheese, 1 cup of banana, eggs, (add the honey here if you're using it instead of sugar), and vanilla. Blend on medium-high speed for 30 seconds, until the mixture is just combined and the cottage cheese curds are no longer visible.
Pour the blended wet mixture over the dry ingredients. Stir gently with a rubber spatula until just combined, when you no longer see dry ingredients.
Let the batter sit in the bowl for 5 minutes to let the oats absorb the moisture and thicken. Then, spoon it into the muffin cups about ¾ of the way to the top. The batter will be airy but thick. If you have any remaining banana and want to decorate the tops with thin slices, do it now.
Bake:
Bake for 25 to 28 minutes, until the tops are brown and a toothpick inserted in the middle comes out clean.
Turn the oven off, crack the door open, and let the muffins sit inside for 5 minutes.This helps them transition from a hot oven into a cold room and prevents sinking. Remove from the oven and cool in the pan for another 5–10minutes before removing.
Storage:
Keep in an airtight container on the counter for 2 days. Refrigerate for up to 5 days, or freeze for up to 3 months. To enjoy, let the muffin come to room temperature or lightly warm it up in the microwave for 20 seconds.
Notes
You can use quick/instant oats for this recipe. You'll need a little more than 2 cups (about 2 ¼ cups) to make 2 cups of oat flour.
A little cornstarch transforms these oat muffins from soft and moist to soft and crumbly. Can be omitted if you don't have any.
Sometimes, these muffins sink slightly as they cool. This usually happens because of the rapid temperature change from a hot oven to a colder room. Or, from excess moisture in the batter from adding more than 1 cup of a banana or too much liquid from the cottage cheese (I recommend holding back as much as possible when measuring).