Garlicky Tortellini Soup

1 tablespoon butter
8 cloves garlic, chopped
4 cups chicken broth
6 ounces cheese tortellini
1 (14 ounce) can diced tomatoes with liquid or
    2 1/2 cups skinned, chopped fresh ripe tomatoes
1 (10 ounce) bag spinach, stems removed
8 to 10 fresh basil leaves, coarsely chopped
Parmesan cheese, grated

Melt butter in a large saucepan over medium-high heat. Add garlic and saut