Using a food processor or blender, combine cream and chiles, adding chipotles a little at a time to taste, and pulse until smooth. Set aside.
Melt butter in a large heavy skillet over medium heat. Saute the green onion, garlic, and salt until soft, about 5 minutes. Add the sliced mushrooms and cook covered, about 3 minutes. Add the tomatoes and bring to a simmer. Reduce heat and cook, an additional 5 minutes. Add shrimp and simmer, covered until they begin to turn pink, about 2-3 minutes. Add broth if additional liquid is needed. Add the chipotle cream and heat until cooked through, an additional 3-5 minutes. Season to taste.
Serve with warm corn tortillas, over rice, or with avocado.
To make broth, combine reserved shells with 2 cups of water and 1/2 teaspoon of salt and bring to a simmer. Continue to simmer over medium heat for 30 minutes. Strain and use broth as needed to add liquid to the dish or thin the cream sauce to desired consistency.
Ana Sofia Pelaez