1. Pre-heat oven to 350 F. Grease and flour a 7" x 11" baking pan.
2. In medium bowl, blend flour, baking powder and baking soda. In large mixing bowl beat sugar and butter till fluffy. Add eggs, Blackberry, Natural Flavor Blend and lemon peel. Beat till creamy. Stir in sour cream. Stir in dry ingredients till blended. Fold in blackberries. Spoon batter into prepared pan and smooth top.
3. In small bowl blend all topping ingredients till crumbly. Sprinkle over batter in pan. Bake cake in 350 F. oven for 40 - 45 minutes or till cake tests done. Serve warm.