Preheat oven to 325 °F. Line a jumbo muffin tin with parchment paper squares or muffin liners.
Peel and mix bananas with sour cream until a smooth paste forms. Set aside.
Cook unsalted butter in a sauté pan on medium-high heat for 4-5 minutes until golden brown.
Remove from heat and add vanilla, 1 tsp cinnamon, nutmeg, ginger, and cloves. Let cool to room temperature.
In a stand mixer fitted with the whip attachment, whip eggs, white sugar, and brown sugar on high speed for 5-7 minutes, or until light and fluffy.
In another large bowl, sift together flour, baking powder, baking soda, and salt. Set aside.
Continue mixing your eggs and sugar on medium speed, slowly drizzling in vegetable oil until fully incorporated and emulsified.
Fold in the dry ingredients and chopped walnuts with a spatula.
Spoon batter into each muffin liner and top with turbinado sugar and the other tsp of cinnamon, divided amongst the tops.
Bake for 35 - 45 minutes until the tops of the muffins spring back when pressed.