8-10cupsapples, peeled and thinly sliced into ¼-inch slices (about 3 to 3½ pounds / 1.4 to 1.6kg) (Honeycrisp, Fuji, or Pink Lady recommended)
¼cuppacked light or dark brown sugar (50g)
2tablespoonsall-purpose flour (15g)
1teaspooncinnamon
1teaspoonvanilla extract
1tablespoonfresh lemon juice
For the Oat Topping
1 ½cupsold-fashioned rolled oats (135g)
⅔cupall-purpose flour (80g)
½cuppacked brown sugar (100g)
1teaspooncinnamon
¼teaspoonkosher salt
½cupunsalted butter, melted (113g)
Instructions
Preheat and Prep: Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch rectangular or oval baking dish.
Make the Filling: In a large bowl, toss the sliced apples with the brown sugar, flour, cinnamon, vanilla, and lemon juice until evenly coated. Transfer to the prepared baking dish and spread into an even layer.
Make the Topping: In a medium bowl, combine the oats, flour, brown sugar, cinnamon, and salt. Pour in the melted butter and stir until the mixture is evenly moistened and clumps together when pressed.
Assemble and Bake: Crumble the topping evenly over the apples in rough, irregular clusters. Cover tightly with foil and bake for 25 minutes until the apples begin to soften.
Remove the foil and bake for 20 to 25 minutes more until the topping is deep golden brown and the apple juices are bubbling around the edges. Let rest for 10 minutes before serving, as the juices will thicken as it sits.
Serve: Scoop into bowls and serve warm with vanilla ice cream or whipped cream.
Notes
Be sure to use sweet apple varieties here like Honeycrisp, Fuji, or Pink Lady, since the added sugar is kept intentionally low and sweeter apples carry more of the sweetness load.
Be sure to slice apples ¼-inch thick or thinner for even baking, as thicker slices won't cook through before the topping browns.