Carrot Soup with Ginger and Lemon

Name: Carrot Soup with Ginger and Lemon
Cuisine: European, British
Ingredients: 1/4 cup (1/2 stick) butter; 1 1/2 cups chopped onion; 1 tablespoon finely chopped peeled fresh ginger; 1 1/2 teaspoons minced garlic; 1 1/4 pounds medium carrots, peeled, chopped (about 3 cups); 2 tomatoes, seeded, chopped (about 1 1/3 cups); 1 1/2 teaspoons grated lemon peel; 3 cups (or more) chicken stock or canned low-salt broth; 2 tablespoons fresh lemon juice; 4 tablespoons sour cream; 1 small carrot, peeled, grated