On a cutting board, cut the baguette in half lengthwise, then slice into 1-inch (2 ½ cm) pieces.
In a bowl, whisk together the eggs, ½ cup heavy cream, the vanilla, and cinnamon.
Add the bread to the egg mixture and stir until evenly coated.
Heat a large cast-iron skillet over low heat. Add the butter, brown sugar, and remaining ½ cup of heavy cream. Whisk to combine and cook until bubbling, about 3 minutes.
Whisk in the peanut butter until fully incorporated and bubbling, about 3 minutes. Add the sliced bananas and stir to coat.
Pour the bread mixture over sauce into skillet and spread evenly.
Bake for 30 minutes, until golden and crispy.
Let the skillet cool for about 5 minutes, then cover with large plate. Holding one hand over the plate, gently flip the skillet upside-down, allowing the French toast to release from the pan with the banana layer on top. Slice and serve.