Preheat oven to 350 degrees F (180 degrees C).
Make the Apple Crisp Filling
In a medium mixing bowl or in the cast iron skillet, mix together the sliced apples, brown sugar, lemon juice, melted unsalted butter, cinnamon, ginger, cloves, nutmeg, and kosher salt together with a wooden spoon.
Mix together cornstarch and cold water with a fork in a separate small bowl, then pour the slurry into your apple mixture. Stir the cornstarch slurry well into the apple filling. If making in a mixing bowl, pour the filling into the cast iron skillet.
Make the Crisp Topping
In a large mixing bowl, add the flour, oats, cold butter, brown sugar, salt, and cinnamon. Use two forks, your fingers, or a pastry cutter to break apart the cold butter and mix it into the flour and oats.
Coat the butter in the dry ingredients and blend it down into the size of peas.
Assemble
Cover the apple filling with the crisp topping in the cast iron skillet. Sprinkle a little extra cinnamon on top for some extra love.
Set the skillet in the preheated oven for 40-45 minutes, until the topping is golden brown.
Let cool for 10 minutes before serving with vanilla ice cream.