In a small saucepan over medium heat, melt butter. Add the vegetables and saute for 4 to 5 minutes. Season with the salt, black pepper and cayenne. Stir in the cream and add the cooked wild rice and the mustard. Combine well and reduce the heat. Simmer until the cream has thickened, about 5 to 7 minutes. Adjust seasoning, if necessary, stir in the parsley and serve immediately.