Preheat the oven to 400°F.
To make the batter: In a medium bowl, add the banana and mash up with a fork.
Add the egg, melted butter, heavy whipping cream, Greek yogurt, and vanilla extract. Mix together.
Add the flour, cane sugar, dark brown sugar, baking powder, cinnamon, nutmeg, and sea salt.
Mix together until a batter forms and there are no dry bits of flour.
Transfer the batter to a piping bag.
Grease the donut pans with avocado oil cooking spray. Pipe the batter into the donut pans.
Bake for 10 to 14 minutes, or until a wooden pick inserted in the center comes out clean. Allow to cool completely in the pans.
To make the topping: In a medium bowl, add the cane sugar and cinnamon.