Preheat the oven to 350 degrees F.
In a small bowl combine the oats, flour, cinnamon, and brown sugar. Cut in the cold butter, then using your hands or fork mix the butter in, until it resembles coarse crumbs. Set aside.
Peel and thinly slice the apples. Layer the apple slices in a cake pan. I like to use a glass 9x13 cake pan, but any rectangle or square pan with still work. Layer the apples on top of each other in the pan, until they are roughly 1/4 inch from the rim of the pan.
Sprinkle the white sugar evenly over the top of the apples.
Sprinkle the prepared topping over the apples, making sure to cover the whole surface area. Try to keep the topping as even as possible.
Bake for 40-45 minutes, or until the topping is golden brown and the apples are bubbly.
Remove the crisp from the oven and allow it to cool for 3-5 minutes before serving. Serve with a scoop of vanilla ice cream, whipped cream, a drizzle of caramel sauce, a drizzle of maple syrup, or on its own.
Enjoy!