Preheat your oven to 350 degrees, grease a 9” cake pan with some non-stick spray, place it on a baking sheet and set aside.
In a small saucepan, to make the caramel layer, add the butter and brown sugar, bring to a simmer and cook just long enough for the brown sugar to melt, about 3 minutes. Remove from the heat and stir in the vanilla and cinnamon.

Pour the sauce in the bottom of the prepared cake pan, arrange the slices of bananas over it and set aside.
In a large bowl, mix together the butter and both kinds of sugar, add the eggs, mashed bananas and vanilla. Using a hand whisk mix everything together until they are somewhat well combined.

Add the flour, baking powder and salt along with the milk and mix until it comes together.
Pour the batter over the banana and caramel layer, carefully transfer to the oven and bake for about 45 minutes (it might take a little more or less time just keep an eye on it) or until fully cooked through.

Remove from the oven, allow it to sit for exactly 5 minutes, then invert it carefully on a platter that has an edge on it so that the caramel doesn’t run off the plate.
Allow it to cool for about an hour then slice and serve!