Preheat your oven to 350°F (180°C) and grease a non-stick donut pan.

In a large bowl, whisk together the all-purpose flour, ground cinnamon, baking powder, baking soda, and fine sea salt.

In a separate bowl, combine melted unsalted butter, granulated sugar, dark brown sugar, buttermilk, sour cream, canola oil, vanilla extract, and mashed ripe banana.

Fold the wet mixture into the dry ingredients gently until just combined.

Fill each donut mold about ¾ full with the batter using a piping bag.

Bake in the preheated oven for 11-12 minutes until they spring back when touched.

Allow donuts to cool in the pan for 5 minutes before transferring to a wire rack.

In a medium saucepan, combine melted unsalted butter, brown sugar, and milk over low heat until smooth. Whisk in powdered sugar to your desired consistency.

In a skillet, melt a tablespoon of butter and add banana slices, sprinkling with brown sugar and cinnamon. Cook until golden and caramelized.

Dip each donut into the warm brown sugar glaze and place on a wire rack. Top with caramelized banana slices.