Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, sugar, baking powder, and salt in a medium bowl; make a well in center of mixture. Place strawberries, milk, oil, vanilla, and egg in a blender; process until smooth. Add pureed strawberry mixture to flour mixture, stirring just until moist.
Coat a waffle iron with cooking spray; preheat. Spoon about 1/4 cup batter per 4-inch waffle onto hot waffle iron; spread batter to edges. Cook 5 to 6 minutes or until steaming stops; repeat with remaining batter. Serve hot with warm Buttered Strawberry Sauce.