Peel, core, and slice the apples evenly. Measure and set aside.
In a mixing bowl, combine almond flour, erythritol, ground cinnamon, and salt. Mix thoroughly to distribute all dry ingredients evenly.
Add the cold, cubed butter to the dry mixture. Use a fork or pastry cutter to cut in the butter until the mixture resembles coarse crumbs, with some pea-sized pieces. The mixture should appear flaky and hold together when pressed.
Preheat the oven to 350°F (175°C). Spread the sliced apples evenly into a baking dish. Top the apples with the prepared crumble mixture, spreading it out evenly across the surface.
Bake in the preheated oven for 20-25 minutes, or until the topping is golden brown and crisp, and the apples are tender and bubbling around the edges. You should hear a gentle bubbling sound and see the topping turn a rich golden hue.
Remove from oven and allow to cool slightly before serving. The crisp should be aromatic, with a crunchy topping and soft, flavorful apples inside.