In a large bowl combine the eggs, oil, buttermilk, and vanilla extract. Add the now-cooled banana mixture and whisk together. Sift the dry ingredients into the wet ingredients and gently fold until combined. Do not over-mix the batter.
Once just combined, pour the prepared pan. Smooth the batter so it's even with the back of a spoon or spatula. Split a ripe peeled banana down the middle vertically before adding it to the top.
Bake for about 45-50 minutes, or until a toothpick inserted comes out clean. Take care not to overbake. Allow it to cool for 30 - 40 minutes in the pan before removing it to cool completely on a wire rack.