0.5 cups unsalted butter – cold, cut into small cubes
pouring custard – for serving
Instructions
Heat the oven to 350°F (175°C) with a rack in the center.
Peel, core, and slice the apples about 0.25 inch thick, then toss in a large bowl with the granulated sugar, lemon juice, ground cinnamon, and cornstarch until evenly coated. Spread the apples in an 8-inch square or similar 2-quart baking dish.
In a separate bowl, combine the all-purpose flour, light brown sugar, and salt. Add the unsalted butter and work it in with your fingertips or a pastry cutter until the mixture forms coarse crumbs with some pea-size bits.
Evenly scatter the crumble over the apples, leaving a few small gaps so steam can escape.
Bake until the topping is deep golden and the juices are bubbling thick at the edges and the apples are tender when pierced, 40–50 minutes.
Let the apple crumble cool for 10–15 minutes so the juices thicken. Serve warm with pouring custard, if using.