Melt butter in a large Dutch oven or soup pot over medium heat. Add shallots then season with salt and pepper and saute until tender, 3-4 minutes. Add garlic then saute for 30 more seconds. Add chicken broth, marinara sauce, and fresh basil then turn heat to high and bring to a boil.
Add tortellini to boiling soup then turn heat down to medium and simmer until the tortellini are tender. Scoop into bowls then serve with fresh bread.