1. 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.
2. Melt butter in a large heavy skillet over medium heat.
3. Sauté the green onion, garlic, and salt until soft, about 5 minutes.
4. Add the sliced mushrooms and cook covered, about 3 minutes.
5. Add the tomatoes and bring to a simmer. Reduce heat and cook, an additional 5 minutes.
6. Add shrimp and simmer, covered until they begin to turn pink, about 2-3 minutes.
7. Add broth if additional liquid is needed. Add the chipotle cream and heat until cooked through, an additional 3-5 minutes.
8. Season with salt and pepper to taste.
9. Serve with warm corn tortillas, over rice, or with avocado.
10. Notes: 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.