Pour batter into prepared pan; spread batter up around sides of pan, completely lining pan and forming a hollow in center of pan. Place blueberries in hollow. Add 1 tablespoon butter and cinnamon to reserved 3/4 cup flour mixture; work mixture with fingers until crumbly. Sprinkle crumbs on top of berries. Bake for 5 minutes. Reduce heat to 350 and bake 20 minutes more. Serve warm or cold.