Combine the flour, brown sugar, maple sugar, rolled oats, salt, cinnamon, nutmeg, and butter in a large mixing bowl of a stand mixer. Combine all of the ingredients well. Set aside.
Spray a 10 or 12-inch cast iron skillet with cooking spray. Or, if you prefer you can use a greased 9x13-inch baking dish.
Peel the apples, core, cut into slices, and toss in lemon juice.
Spread the apple slices in the bottom of the skillet or baking dish. Cover with apple crisp topping.
Cover the skillet or baking dish with aluminum foil.
Place the cast iron skillet or baking dish on a half sheet pan lined with parchment paper. This will help catch any juices that overflow.
Bake in a preheated 375 degree F oven for about 60 minutes.
Towards the very end of the baking process, maybe the last 10 minutes, remove the aluminum foil and let crisp up the top. The apple filling should be bubbling up around the edges.
Remove from the oven when apple juices are bubbling up around the edges. Let cool for 10-15 minutes before serving.
Serve with vanilla ice cream and drizzle with caramel sauce if desired.
Notes
We love using granulated maple sugar. If needed; substitute sugar in the raw or granulated white sugar.