Toss the blueberries with cinnamon and lemon juice.
Place in a greased 8-in. 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° for 45-50 minutes or until the cake tests done.