Whisk together flour, ¼ cup sugar, baking powder, and ½ tsp. salt in a large bowl; add butter, and using your fingers, rub butter into flour until pea-size crumbles form. Add milk, and stir just until a moist dough forms; cover and refrigerate dough until ready to use.
Heat oven to 400°. Bring remaining sugar and salt along with blueberries and citrus juices to a boil in a 12? cast-iron or enamelware skillet over high heat, stirring to dissolve sugar. Remove pan from heat, and using two tablespoons, portion and form chilled dough into 2 to 3? oval dumplings, and drop them evenly on top of the blueberry mixture. Sprinkle dough dumplings with sugar, and transfer skillet to oven; bake until biscuits are cooked through and blueberry mixture is reduced, about 25 minutes. Serve hot with vanilla ice cream, if you like.