By An Edible Mosaic
Prep the apples. Peel and core the apples, and then cut them into 1/4-inch thick slices.
Make the filling. Add the sliced apple to a large bowl and toss with the lemon juice to coat. Stir in the sugar, flour, cinnamon, and nutmeg and gently toss to coat the apples. Let the apples sit until they start seeping liquid, about 45 to 60 minutes.
Make the topping. Mash the butter and stir in the brown sugar and salt. Stir in the flour and oats and until the mixture is crumbly. You can use a fork, but this works best if you combine the mixture with your fingertips.
Assemble. Pour the apple filling (including the juice) into a 9 by 13-inch baking dish and spread it out evenly. Sprinkle the crumble topping evenly on top.
Bake and enjoy. Bake at 375F until the crisp is golden on top and bubbling around the outside, about 30 to 35 minutes.