Preheat the oven to 425 degrees F (220 degrees C). Divide butter between 2 shallow 1-cup oven-proof dishes and heat in the oven until butter melts.
Stir blueberries, brown sugar, lemon juice, and cinnamon together in a bowl and toss to combine.
Combine milk, eggs, flour, and salt in a bowl. Mix well. Divide batter evenly between the prepared dishes. Add blueberry mixture and sprinkle blueberries evenly on top.
Bake in the preheated oven until puffed and golden, 17 to 20 minutes.
