Simmer shallots, parsley sprigs, and mushrooms in butter for about 2 minutes. Add clam juice and wine and bring to a boil. Reduce heat and simmer 5 minutes. Remove parsley sprigs. Add frozen shrimp to liquid. Heat gradually, breaking shrimp apart as they heat. Once to boiling stage, reduce to a simmer and cook for 2 minutes. Season with salt and pepper.