Bring a pot of salted water to a boil.
Peel and cut the plantains in half crosswise. Boil the plantains until soft, 10 to 15 minutes depending on ripeness.
Drain the water or reserve for another use. (Kelis sets aside the plantain cooking water to thin out the sauce in her Jumbo Shrimp with Tomato Fricassee and Strawberries recipe.) Add the butter to the plantains and mash with a potato masher, then add the warmed whipping cream. Combine until smooth, and add salt and pepper to taste.