Prep: Generously butter a 9x13 casserole dish with 1/2 Tbsp butter. Preheat the oven to 375F.

Cut Apples: Peel, core, and thinly slice apples to 1/4’ thickness. You should have 12 cups of sliced apples. Squeeze 2 Tbsp lemon juice over the apples and toss to coat.

Make Apple Filling: In a separate bowl, stir together 3/4 cup sugar, 3 Tbsp flour, and 1 1/2 tsp cinnamon, then sprinkle mixture over apples and toss to combine. Transfer apples to the buttered casserole dish.

Make the topping: in a large bowl, use your hands to stir together flour, oats, brown and granulated sugars, cinnamon, and salt. Add the diced butter and work it into the mixture with your hands until pea-sized crumbs form throughout. Spread topping over apples.

Bake at 375˚F for 45-50 minutes or until the topping is golden and crisp and the apples are bubbling with thick juices at the edges and the apples are tender when pierced with a knife.