Preheat and prepare the pan. Heat your oven to 350°F (175°C). Lightly butter a 9-inch square baking dish or similar 2-quart dish.

Peel and slice the apples. Peel apples, core them, and slice about 1/4-inch thick. You should have roughly 8 cups of slices. Thinner slices soften more; thicker slices keep more bite.

Toss the filling. In a large bowl, combine apples with 1/3 cup granulated sugar, 1 tablespoon brown sugar, 2 tablespoons flour, 1 teaspoon cinnamon, a pinch of nutmeg (optional), 1 tablespoon lemon juice, 1 teaspoon vanilla extract (optional), and a pinch of salt. Toss until evenly coated, then spread in the prepared dish.

Make the crumble. In another bowl, mix 1 cup all-purpose flour, 1/3 cup granulated sugar, 1/3 cup light brown sugar, 1/2 teaspoon cinnamon, and 1/4 teaspoon salt. Add 1/2 cup (1 stick) cold unsalted butter cut into small cubes.

Cut in the butter. Use your fingertips or a pastry cutter to rub the butter into the dry ingredients until the mixture forms clumps and pea-sized bits. Don’t overwork; you want a crumbly texture, not a dough.

Top the apples. Scatter the crumble evenly over the apple layer, leaving some uneven spots for texture. Don’t press it down; air pockets help the topping crisp.

Bake. Place on a middle rack and bake 40–50 minutes, until the apples are bubbling and the topping is deep golden brown. If the top browns too fast, tent loosely with foil for the last 10 minutes.

Rest before serving. Let the crumble cool for at least 15 minutes. This helps the juices thicken so the filling sets nicely.

Serve. Enjoy warm with vanilla ice cream, whipped cream, or a drizzle of heavy cream.