In a large shallow bowl or dish, whisk together eggs, milk, vanilla, salt, cinnamon, and allspice. Soak as many slices in the egg mixture as possible for 5 minutes, turning once.
Heat 1 tablespoon of the butter and 1 tablespoon of the oil in a very large saute pan or griddle over medium heat. Add the soaked bread and cook for 2 to 3 minutes per side, until well browned. Add more butter and oil to the pan as needed. Once all the bread is cooked, place it on a baking tray in the warm oven.
Make the Topping:
In a small skillet, melt the butter. Add the brown sugar and stir until dissolved. Add banana slices to the pan, stirring so they are covered in caramel sauce. Sprinkle a pinch of cinnamon. Bananas are done when they are warmed through. Pour bananas foster mixture over French Toast.