Peel, core, and thinly slice the apples. Toss them with lemon juice to keep their color bright while you prepare the other ingredients.
In a large mixing bowl, combine 1 ½ cups of flour, half the sugar, cinnamon, nutmeg, baking powder, and salt. Stir together until evenly mixed.
Add the melted butter and vanilla extract to the dry ingredients. Mix with a spoon or spatula until the mixture resembles coarse crumbs—it should be crumbly but hold together when pressed.
Pour the remaining ½ cup of flour, the rest of the sugar, cinnamon, and a pinch of salt into another bowl to make the crumble topping. Cut in the cold butter with a pastry cutter or your fingers until the mixture is crumbly and resembles coarse sand.
Spread the sliced apples evenly at the bottom of a greased baking dish, creating a compact layer.
Sprinkle the prepared crumble mixture generously over the apples, covering them completely with a crunchy, spiced layer.
Bake in a preheated oven at 350°F (175°C) for about 45 minutes, or until the top is golden brown and crisp, and the apples are bubbling underneath.
Remove from oven and let cool slightly to allow the juices to settle.
Serve warm or at room temperature, perhaps with a scoop of vanilla ice cream or a dollop of whipped cream if desired.
