Preheat oven to 350 degrees F (175 degrees C). Grease doughnut pan.
Whisk All-Purpose Flour (1 1/4 cup), Baking Powder (2 teaspoon), Salt (1/2 teaspoon) and Ground Cinnamon (1 1/2 teaspoon) together.
In a separate bowl, combine Brown Sugar (1/2 cup), Egg (2), Banana (2), Vanilla Extract (2 teaspoon) and Canola Oil (1/2 cup). Add this combination to the dry ingredients. Stir until just combined.
Spoon batter into greased doughnut pan about 3/4 full. Bake for 12 minutes. Place on wire rack to cool completely.
Heat Salted Butter (2 tablespoon) over medium-high heat until melted and bubbling and spitting have stopped, about 3-4 minutes.
Remove from heat and add Peanut Butter (1/2 cup) to the pan and stir. Add Powdered Confectioners Sugar (1/2 cup) and Milk (2 tablespoon) or water. Stir until smooth.
Dip smooth bottom of doughnuts into frosting and enjoy!