Preheat oven to 350°F. Spray a 9x13-inch pan with nonstick cooking spray.
Peel, core, and slice apples. I like to cut them into thin slices, but you can cut them however you want. Sprinkle with about 1 teaspoon of lemon juice to prevent too much browning.
Place apple cider in a 12-inch skillet over medium-high heat. Bring to a boil and cook until it reduces by half, approximately 5-8 minutes. Remove cider from pan.
Place butter in the pan over medium heat and melt. Add apples, sugar, and cinnamon. Stir to coat apples. Cook, stirring occasionally, until apples just begin to soften (about 10-15 minutes depending on the size and thickness of your apples). You don't want them fully cooked, just partially (a little firmer than when you do a fork test to a potao).
While apples are cooking, add brown sugar, cinnamon, salt, flour, and oats to a medium sized bowl Stir to combine. Add melted butter and stir with a fork until thick and crumbly.
Once apples are done, add the reduced cider and apples to prepared pan. Sprinkle with crumble topping.
Bake for about 20-25 minutes, or until crumble is lightly browned around the edges.
May be made a day in advance. Refrigerate overnight. Serve with whipped cream or ice cream.