Boil potatoes separately, then simmer until fork tender (approximately 10 min).
Remove 1/4 cup sweet potato liquid and 1/3 cup white potato liquid.
Beat white potatoes, 1/2 cream cheese, salt and pepper and reserved liquid until smooth. Repeat with sweet potatoes.
In shallow 2 1/2 qt baking dish, alternately dollop white and sweet potatoes by cupfuls. Cut and twist with knife to create marbled look.
Bake covered @ 350 degrees for 40 minutes.
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