Preheat your oven to 350 degrees.

Grease a 9x13 baking pan with coconut oil or butter. Set aside.

In the bowl of your stand mixer beat the granulated sugar and room temperature butter until creamed together. This will take 3-4 minutes. 

Add the mashed bananas, coconut oil, brown sugar, eggs, vanilla and sour cream to this mixture. Mix until blended together.

Add the flour, xanthum gum, baking powder, baking soda, cinnamon and salt. Blend the batter just until the dry ingredients are mixed with the wet ingredients. Don't over blend! 

Pour the cake batter into the greased 9x13 baking pan. 

Bake at 350 degrees for 35-40 minutes. The cake will be browned and firm, but slightly spongy to the touch.

Let the cake cool for 10-15 minutes. Then place parchment paper on top of a baking sheet and invert the cake onto this. Skip this step if you want to frost the cake as is in the pan. 

Let the cake cool completely before frosting. I used my Gluten Free Chocolate Buttercream Frosting recipe.