PREHEAT oven to 350° F. Grease 9-inch-square baking pan.
COMBINE baking mix and dry milk in small bowl. Beat 1/3 cup butter, 1/4 cup brown sugar and 1/4 cup granulated sugar in large mixer bowl until creamy. Add eggs and water; beat on medium speed for 2 minutes until blended. Gradually beat in baking mix mixture just until blended.
COMBINE remaining 1/4 cup brown sugar, 2 tablespoons granulated sugar, 1 tablespoon butter and cinnamon in small bowl.
SPREAD batter into prepared pan. Sprinkle cinnamon-sugar mixture over batter. Poke round end of wooden spoon randomly into batter to form streusel ribbons in cake.
BAKE for 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool in pan on wire rack. Serve warm. Store any remaining cake tightly covered.