Blueberry Streusel Treats

Sift flour, baking powder and salt together. In large bowl cream butter with sugar until fluffy. Beat in egg with vanilla. Stir in flour mixture alternately with milk. Fold in blueberries. Place a paper baking cup in each of 12 large muffin pan cups. Spoon batter into cups, filling each about 2/3 full. In small saucepan, melt margarine. Remove from heat. Stir in brown sugar, cinnamon, and walnuts. Sprinkle streusel topping over muffins. Bake 400F oven for 20 minutes or until tops spring back when lightly pressed with fingertip. Remove from pan; cool on wire rack.