Preheat the oven to 350ºF (180ºC) and have a 4 to 6 quart (4 to 6 L) cast iron Dutch oven ready.
Make the oat topping first. In a mixing bowl, combine the flour, brown sugar, oats, cinnamon, and salt. Stir well, then add the butter. Using your hands, a pastry cutter, or a fork, blend the butter into the dry ingredients until the mixture is coarse and crumbly. Place the bowl in the freezer to chill while you prepare the apples.
Core and peel the apples. Chop them into chunks about ½ inch (2.5 cm) thick and add them directly to the Dutch oven. Add the lemon juice and stir, then add the sugar, flour, cinnamon, and cardamom. Stir until the apples are well coated.
Remove the topping from the freezer and scatter it evenly over the apples. Place the Dutch oven in the oven with the lid off and bake until the topping is golden and the filling is bubbling, about 50 to 55 minutes.
Cool the apple crisp on a wire rack for 10 minutes before serving warm with ice cream or whipped cream.
Notes
For detailed ingredient notes, substitution tips, variations, and step-by-step photos, scroll through the full recipe post.
Use a digital kitchen scale for precise measurements and an oven thermometer to confirm your oven is heating correctly.
Stir the dry ingredients for the topping thoroughly before adding the butter to avoid floury pockets.
Check the crisp after 50 minutes of baking and keep an eye on it until the topping is golden and the filling is bubbling.
Storage
Store leftovers covered in the refrigerator for up to 3 days. You can reheat the crisp in the oven at 350ºF (180ºC) for 15 to 20 minutes until warmed through, or in the microwave.