Preheat oven to 350 degrees and place a skillet (I used an 10.5" square cast iron skillet) on the stovetop over medium high heat.
First peel and slice your apples, then place them in a bowl and toss with sugar, vanilla, cinnamon and corn starch.
Heat apples into hot skillet and cook for about 5 minutes until softened and sugar has dissolved.
In a separate medium-large bowl combine oats, flour, brown sugar, butter, remaining cinnamon and salt. Mix well.
Place oat mixture on top of apples in the skillet, or you can transfer the apples to a baking dish at this time if you prefer to make your crisp without the skillet. Press oat mixture down slightly to pack.
Cover your skillet or baking dish with aluminum foil at bake for 20 minutes with the foil, the remove and bake for an additional 15-20 minutes.
Crisp is done when the top is golden brown and the apples are bubbling!
Serve with vanilla ice cream, if desired, and enjoy warm!