PREPARATION:

1. Preheat oven to 350°F. Lightly grease 30 standard (2-1/2-inch) muffin pan cups or line with paper baking cups.
2. For cupcakes, combine 2 cups flour, baking powder and salt in medium bowl; mix well. Set aside. Beat granulated sugar and 1/2 cup butter in large bowl with electric mixer at medium speed 1 minute. Add milk and vanilla. Beat at low speed 30 seconds. Gradually beat in flour mixture; beat at medium speed 2 minutes. Add egg whites; beat 1 minute. Spoon batter into prepared muffin cups, filling 1/2 full. Spoon blueberries over batter. Bake 10 minutes.
3. Meanwhile for streusel, combine 1/3 cup flour, oats, brown sugar and cinnamon in small bowl; mix well. Cut in 1/4 cup butter with pastry blender or two knives until mixture resembles coarse crumbs. Stir in chopped nuts.
4. Sprinkle streusel over partially baked cupcakes. Return to oven; bake 18 to 20 minutes or until golden brown and toothpicks inserted into centers come out clean. Cool in pans on wire racks 10 minutes. Remove cupcakes to wire racks; cool completely. (Cupcakes may be frozen up to 3 months.)