In another saucepan, add cream, chicken broth, flour, salt, mustard & cayenne pepper. Whisk together to incorporate all ingredients. Bring to a boil, whisking often then turn down heat & continue cooking until thick, whisking for about 8 minutes. Turn off heat & add remaining 1/2 Tbsp margarine along with the vegetable mixture. Blend well, taste & adjust seasoning if necessary. Set aside.