Prepare your campfire or camp stove. You need a steady medium heat. For a campfire, let it burn down to hot coals. For a stove, set to medium.
In a 10-inch Dutch oven or heavy pot with a tight-fitting lid, combine the berries, 1/4 cup sugar, and lemon juice. Stir gently. Place the pot over the heat and bring to a simmer. Cook for 5 minutes, stirring occasionally, until the berries release their juices and the mixture thickens slightly. If using frozen berries, cook for 7-8 minutes.
While the berries simmer, make the biscuit topping. In a medium bowl, whisk together the flour, 2 tablespoons sugar, baking powder, and salt. Add the cold butter cubes. Using your fingertips or a fork, work the butter into the flour mixture until it resembles coarse crumbs with some pea-sized butter pieces remaining.
Add the milk and vanilla extract to the flour mixture. Stir just until a soft, shaggy dough forms. Do not overmix. The dough will be sticky.
Remove the pot from the heat. Drop spoonfuls of the biscuit dough evenly over the hot berry mixture. You should have about 6-8 dollops. Do not stir them in.
Cover the pot with its lid. Return the pot to the heat. For a campfire, place the pot on a bed of coals and add a few coals on top of the lid. For a stove, keep the heat on medium-low. Cook for 10 minutes without lifting the lid. The biscuits will steam and become fluffy.
After 10 minutes, remove the pot from the heat. Let it rest, covered, for 2 minutes. Uncover and check that the biscuits are cooked through (a toothpick inserted into a biscuit should come out clean).
Serve warm directly from the pot. Spoon into bowls or mugs. For an extra treat, top with a dollop of yogurt or a splash of cream if you have it on hand.