Preheat oven to 325°F. Spray a 13x9-inch baking dish or cake pan with baking spray or butter and flour. Set aside.
In a large bowl use a whisk to sift together the flour, baking powder, baking soda, cinnamon and salt.
In a separate medium mixing bowl whisk together granulated sugar, brown sugar, vegetable oil, sour cream, eggs and vanilla extract until sugar has dissolved. Whisk in mashed banana until well blended.
Add wet ingredients to the flour mixture whisking until fully combined. Pour cake batter into prepared pan.
Bake for 40-45 minutes or until a cake tester or toothpick inserted into the center shows moist crumbs.
Cool completely on a wire rack or in the fridge.
Cream Cheese Frosting: In a medium size mixing bowl using an electric mixer beat together cream cheese, butter and vanilla extract. Gradually add powdered sugar. Add cream or half and half 1 Tbsp at a time to thin as needed.
Frost the cooled cake then sprinkle with toasted pecans or walnuts. Store chilled covered with plastic wrap.
Toasting Nuts: Spread pecans in a single layer on a baking sheet. Toast in a preheated 350°F oven for 6-8 minutes until lightly golden brown and fragrant. Set aside to cool.