Apple Banana Upside-Down Cake

This cake is the best of both worlds! It's bursting with so much flavor from the caramelized apples on top, to the bananas laced throughout. It gets cooked directly into a cast-iron skillet with a quick caramel sauce, and then flipped out for a beautiful presentation. Enjoy!
 
INGREDIENTS:
10 Tbsp unsalted room temp butter, divided
¼ cup light or dark brown sugar, packed
1/2 tsp kosher salt 
3 large bananas, divided 
2 small or 1 large apple (we used pink lady)
½ cup white sugar 
½ cup light or dark brown sugar
2 large eggs
¾ cup full fat Greek yogurt 
1 tsp vanilla extract 
1 ¼ cups all-purpose flour 
1 tsp cinnamon 
¾ baking soda
¾ baking powder
½ tsp nutmeg 
½ tsp kosher salt 
 
INSTRUCTIONS:
Preheat oven to 350 degrees. 
 
Melt 4 tablespoons butter in a well-seasoned 10-inch cast iron skillet. Add brown sugar and salt, and stir until sugar is melted and combined. Remove from heat. 
 
Core and slice the apples and cut into thin wedges. Arrange over the butter sugar mixture. Cut one of the bananas in half crosswise and then in thirds, to create 6 pieces. Layer over the apples. 
 
Place the two remaining two bananas in a separate bowl and mash. Set aside.
 
Prepare the batter by combining sugars and remaining 6 tablespoons butter in the bowl of an electric mixer. Beat until light and fluffy, about 5 minutes. Reduce speed and add eggs one at a time, then mashed banana, yogurt, and vanilla. Mix until well combined. 
 
In a separate bowl combine flour, cinnamon, baking soda, baking powder, nutmeg, and salt. 
Slowly mix dry ingredients into wet ingredients, and mix just until you no longer see flour. Pour batter into skillet over the bananas. 
 
Bake on middle rack in oven until golden brown, about 40 minutes. Remove and allow to cool before inverting cake. To remove from pan run a butter knife around the edge of cake then invert the cake onto a large plate.