1. Combine first 6 ingredients in a large saucepan; bring to a boil. Reduce heat, and simmer 30 minutes. Place half of tomato mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Pour into a large bowl. Repeat procedure with remaining tomato mixture. Stir in salt and pepper. Ladle 3/4 cup soup into each of 6 bowls; top each serving with 1 tablespoon yogurt and 1 1/2 teaspoons basil.