3. To make the cake, whisk together the flour(s), baking powder, salt and cinnamon,in a small bowl and set aside.
4. In the bowl of a stand mixer fitted with the paddle attachment, or by hand in a medium bowl using a sturdy spatula, beat the butter with the granulated sugar until light and fluffy. Add the eggs one at a time, stopping the mixer between the additions and scraping down the sides.
5. On slow speed, mix in half of the dry ingredients, then the milk and vanilla, then the rest of the dry ingredients, mixing only until they’re just incorporated. Do not overmix. Scrape the batter over the bananas in the skillet and bake the cake for 30 to 35 minutes, until the cake feels done when you press it in the center. A toothpick inserted into the center should come out relatively clean.
6. Remove the cake from the oven and let stand for 10 minutes. Run a knife around the outside of the cake to help it release from the pan, and turn it out onto a serving platter or cooling rack, wearing oven mitts and taking care to avoid drips from hot caramel. Any caramel bits that may have stuck in the pan can be spooned back over the warm cake.