For the apples, select tart, crisp ones to balance the sweetness of the topping. Gravenstein, Pippin, and Braeburn are all good choices.
Preheat the oven to 375°F . Have ready an unbuttered 2-inch deep 2-quart baking dish.
Peel, core, and cut 2 1/2 pounds tart apples (about 8 medium) into 1-inch chunks.
Spread the fruit evenly in the baking dish and toss with 1/4 cup sugar, 2 tablespoons lemon juice, and 1 tablespoons cornstarch or tapioca starch.
Combine 3/4 cup all purpose flour, 1/2 cup packed brown sugar, 1 teaspoon ground cinnamon, 1/2 teaspoon salt and 1/4 teaspoon grated or ground nutmeg.
Add in 1 stick cold unsalted butter, cut into small pieces or pulse until the mixture resembles coarse bread crumbs. If desired, stir in 1/2 cup sliced almonds.
Scatter the topping evenly over the fruit. Bake until the topping is golden brown, the juices are bubbling, and the apples are tender, 50 to 55 minutes. Serve hot or at room temperature.