Prepare your campfire or camp stove. For campfire cooking, let the fire burn down to a bed of hot coals—this gives steady, even heat. For a camp stove, set it to medium-low heat.

In a bowl or ziplock bag, combine the flour, sugar (reserve 2 tablespoons for the berries), and cinnamon. Add the cold butter cubes. Use your fingers or a fork to mix until the mixture resembles coarse crumbs. This is your crumble topping.

Place the blackberries in a greased Dutch oven or cast iron skillet. Sprinkle the reserved 2 tablespoons of sugar over the berries and toss gently.

Sprinkle the crumble topping evenly over the blackberries. Do not stir—the topping should sit on top to create a crust.

Cover the Dutch oven or skillet with its lid. If using a skillet without a lid, cover tightly with heavy-duty aluminum foil.

Cook over the campfire or camp stove: For campfire, place the pot on a few hot coals and add a few coals on top of the lid. For camp stove, cook on low heat, checking occasionally. Cook for 25-30 minutes, until the berries are bubbling and the topping is golden brown. Rotate the pot every 10 minutes for even cooking.

Carefully remove from heat using oven mitts or a campfire glove. Let it cool for 5 minutes before serving. Enjoy warm, plain or with a dollop of yogurt or ice cream if you have it.