Step 1 Stir brown sugar and cinnamon together in small bowl. Add butter; stir until blended. Set aside.
Step 1 Lightly grease and flour 9 x 13-inch (23 x 33 cm) baking pan. Set aside.
Step 2 Beat butter and sugar in large bowl with electric mixer until blended. Add eggs and vanilla; beat until blended.
Step 3 Stir flour, baking powder and salt together in medium bowl. Add a third of flour mixture to egg mixture; beat just until blended. Add half of milk mixture, beat just until blended. Continue alternating flour mixture and milk until both are incorporated into batter. Add blueberries; mix batter gently by hand just until combined. Spread batter into prepared baking pan. Sprinkle topping evenly over batter.
Step 4 Bake in preheated 350˚F (180˚C) oven until toothpick inserted near centre of cake comes out clean, 40 to 45 minutes.