Preheat oven to 375°F.
Cream together the sugar, butter, sour cream, and egg.
Add mashed bananas and vanilla extract.
Sprinkle on the flour, followed by the salt and baking soda, using a spatula to incorporate well.
Pour into a greased 8x8 pan.
Sprinkle the turbinado sugar evenly over the top of the cake before baking for 20-25 minutes or until a toothpick inserted in the center comes out clean.