Banana Cake:

1. Pour 1 tablespoon of vinegar into a 1-cup measuring cup and pour enough milk to make 1 cup. Let sit for milk to sour. Milk may begin to look curdled, but it will be fine.
2. Into a mixing bowl, beat coconut oil and sugar together until fluffy. Add eggs, one at a time, and beat until thoroughly incorporated. Mix in mashed bananas and vanilla.
3. In a small bowl, mix together all-purpose flour, coconut flour, baking soda, and salt. Turn the mixer back on and slowly add half the flour mixture. Slowly pour in the soured milk and then add the rest of the flour mixture, mixing just until combined. Do not over-mix.
4. Take a rubber scraper and scrape the sides and bottom of the mixing bowl to make sure everything is well incorporated. Set aside while you prepare the salted caramel and preheat oven to 350ºF

Salted Caramel:

1. Place a 9-inch springform pan onto a cookie sheet and set aside.
2. In a small saucepan, begin to melt butter and coconut sugar over medium-low heat, stirring constantly with a fork or whisk. Coconut sugar burns easily, so make sure that your heat isn’t too high. When the sugar begins to melt, stir in the maple syrup, which will help to bring the sauce together.
3. Pour hot caramel into the bottom of the springform pan and quickly spread to coat before it cools. Cut the ripe banana into thin slices and place in concentric circles on top of the caramel. Carefully pour the cake batter on top of the bananas and caramel. Place springform pan along with cookie sheet into the middle rack of the preheated oven. Bake for 40-50 minutes or until center of cake is set and a toothpick inserted near the center comes out with only a few moist crumbs. It will appear very brown, but that is due to the dark color of the coconut sugar. Let cake cool slightly.
4. Use an offset spatula to release cake from the edge of the springform pan. Carefully remove the side of the springform pan and invert the cake onto a serving platter. Use the offset spatula, if necessary, to remove the bottom of the pan from the cake. Cake is best if served immediately.