1) Preheat oven to 180C/Gas 4.
2) Combine berries, cinnamon and lemon juice in a 23-by-33 cm baking pan.
3) Combine flour, 3/4 cup sugar and baking powder in a medium mixing bowl and stir. Add milk and butter while stirring. Pour mixture over berries until covered.
4) Combine cornflour and 1/2 cup sugar in small mixing bowl and stir. Sprinkle mixture over batter.
5) Remove boiling water from heat and slowly pour over entire pan. Place baking pan into oven and bake for 45 to 50 minutes or until crust is golden brown. Remove from oven, allow to cool slightly.