Preheat oven to 350 degrees F (180 C).
Toss apples with the lemon juice, ⅓ cup sugar, cinnamon, cardamom, and salt in a large bowl.
Heat 2 tablespoons of butter over medium heat in a large saucepan. Brown the butter (usually takes 3 minutes) and add the apples.
Sauté the apples for 5 minutes and stir only occasionally and very gently.
Put apples in a baking dish that can hold at least 6 cups.
For the crisp top, combine the remaining butter, almond flour, oats, and ⅓ cup sugar in a medium bowl and with your hands or a pastry cutter, combine till pea-sized pieces have formed.
Spread the topping evenly over the apples.
Bake for 45 minutes or until the crumble top is golden brown.
Serve immediately (with optional vanilla ice cream) or store in the refrigerator for up to 3 days.