Preheat oven to 350 degrees. Grease a deep dish pie plate or large baking dish with butter or cooking spray and set aside.
Combine the sliced apples with the sugar, cinnamon, and vanilla extract in a large bowl and mix until all of the apples are evenly coated. Pour into the prepared baking dish.
In a separate medium size bowl, combine the flour, oats, brown sugar, salt, and cinnamon. Pour in the melted butter and stir until well coated and crumbly. Sprinkle the crumb mixture evenly over the top of the apples.
Bake in the preheated oven for 45-60 minutes until fruit is soft and the topping is golden brown. Allow to cool slightly before serving. Serve warm with vanilla ice cream on top. Enjoy!
Slice your apples evenly. I slice my apples using this slicer to speed up the process and remove the core easily. I then slice the apples one more time each with my knife so that the widest part of the slice is roughly 1/2 an inch wide. You can also chop them into big chunks if you would prefer, but just make sure that you chop your apples to a uniform size to ensure even baking in your apple crisp.
Prevent over-browning. If your topping is starting to get too brown but your apples still need more time to cook, simply place some aluminum foil loosely over the top of your pan and continue baking.
Optional additions: Chopped nuts like pecans or walnuts would be a delicious addition to the topping! I didn't add any to ours because my son has a nut allergy.
Serving: this apple crisp tastes AMAZING with a scoop of vanilla ice cream on top! You could also top it with whipped cream and a drizzle of caramel sauce. Yum!