Old Fashioned Banana Cake

very ripe bananas, mashed

granulated sugar

light brown sugar, lightly packed

vegetable oil

extra-large eggs, at room temperature

sour cream (I used low fat)

vanilla extract

all-purpose flour, after sifting

baking soda

kosher salt

powdered sugar for sprinkling on top

coarsely chopped walnuts (optional)

Cream cheese frosting ( optional,recipe follows)

Walnut halves, for decorating