Using a mixer, cream together the butter, oil, and sugar.
Add the eggs, banana, and vanilla, and mix well.
Add the mayonnaise and mix.
Combine the dry ingredients in a small bowl, then add, mixing until thoroughly incorporated.
Spread the batter in a greased 9 x 13 inch pan.
Bake at 350° for 30 – 35 minutes.
Cool in the pan, or turn onto a rack if desired.
This cake is good with a simple glaze, cream cheese frosting, or vanilla frosting. It’s also great plain. I’m sure there are many ways to mash bananas, but my favorite is to put them in a small bowl and use a pastry blender to mash them.
Recipe by The Gluten-Free Homemaker at http://glutenfreehomemaker.com/banana-cake-whats-for-dinner-wednesday/