Preheat the oven to 350ºF. Prepare a 10 or 12 inch skillet or 9 by 13 inch baking pan.

Prepare Apples: Peel and chop or slice apples. Place in a cast-iron skillet. Add brown sugar, cornstarch, cinnamon, lemon juice, vanilla extract and salt to the apples. Stir gently until roughly combined.

Pre-Cook Apples: Place the skillet over medium heat on the stove and cook apples, stirring every few minutes for about 10 minutes. The apples will begin to soften.

Top Apples: While the apples are softening, mix up the sourdough crumb topping. To a small bowl whisk together sourdough discard and melted butter until combined. Add brown sugar, cinnamon and salt. Mix again. Give the rolled oats a whirl in the blender to break down just a bit if desired. Add flour and oats and mix. The topping will be a little bit sticky - that's normal. Take chunks of the oat topping and spread on top of the warm apples, spreading the topping out until it evenly covers most of the apples.

Bake: Place skillet in the oven and bake for about 40 minutes until apples are bubbling and oat crisp is baked through.

Caramel Sauce: While the apple crisp bakes, make the caramel sauce. To a heavy-bottomed pot, add the butter, brown sugar, heavy cream and salt. Turn stove onto medium-low heat and let the ingredients melt together. Stir gently until ingredients are just combined. Once ingredients are combined, turn the heat to medium and don't stir! Let the caramel bubble for about 7-10 minutes until it reaches 225ºF. Then remove from the heat and add vanilla extract. Set aside to thicken and cool. If you really love caramel sauce, double this batch and store some in the refrigerator for later!

Drizzle caramel sauce over the entire sourdough apple crisp or serve the caramel sauce on the side for individual portions. Enjoy warm!