In a medium bowl, toss blueberries with 1/3 cup sugar and lemon juice. Let sit while you prepare the dough.
In a separate bowl, whisk together flour, 2 tablespoons sugar, baking powder, and salt. Cut in cold butter using your fingertips or a fork until the mixture resembles coarse meal. Stir in milk just until a soft dough forms — do not overmix.
Lightly oil a 2-quart Dutch oven or heavy pot. Pour the blueberry mixture into the pot and spread evenly. Drop spoonfuls of dough over the berries — about 8 small dollops. Sprinkle the remaining 1 tablespoon sugar on top.
Cover the pot with its lid. Place on a camp stove over medium-low heat (or on a grate over a low campfire with coals underneath). Cook for 20-25 minutes, until the dough is cooked through and the berries are bubbling. Rotate the pot once or twice for even heat.
Remove from heat. Let rest, covered, for 5 minutes. Serve warm, directly from the pot. Spoon into bowls or eat straight from the pot with spoons.