In a non-reactive 2 quart saucepan heat milk and cream to a boil and immediately remove from heat. Add juice, zest, salt and sugar, stir well and allow to stand 20 minutes. Line a conical sieve with cheesecloth and pour tepid mixture through, allowing the whey to drain through. (Save this for your pet). Allow to stand at room temperature for 2 hours and press lightly to form conical shape. Turn out onto plate and cover with wax paper. This is best eaten the day it's made but will last several days in the refrigerator.