Pour 1/2 of melted butter into cast iron skillet or round cake pan.
Swirl pan until bottom and sides are well-coated with butter to prevent cake from sticking.
Sprinkle brown sugar evenly over the melted butter in the skillet or cake pan.
Place apple slices on top of the brown sugar.
In a separate bowl, combine buttermilk, the remainder of your melted butter, eggs, sugar, flour, baking soda, salt, and cinnamon.
Whisk together until well-combined.
Pour evenly over the apples and brown sugar layer in the skillet or cake pan.
Place in the oven and bake for approximately 45 minutes to 1 hour or until toothpick or skewer inserted in the center comes our clean. You can follow my tips for how to tell when your cake is done.
Allow to stand for about 5-10 minutes before transferring to a cake stand
When ready to transfer, place cake stand on top of skillet then carefully flip to where the cake comes out onto the cake stand.