Toss blueberries with the cinnamon and lemon juice, place in a greased 8-inch square baking dish.
In a bowl, combine flour, sugar and baking powder; stir in milk and butter. Spoon over berries.
Combine sugar and cornstarch; sprinkle over batter. Slowly pour boiling water over all. Bake at 350 degrees for 45-50 minutes or until the cake tests done.