To prepare pudding: Combine sweet potato, water, 3 tablespoons each granulated sugar and brown sugar, 1 tablespoon butter, orange zest, orange juice, lemon zest, lemon juice and salt in small saucepan. Bring to a boil over high heat. Reduce heat to low, cover and simmer until the sweet potato is very tender, 15 to 25 minutes. Let cool for 5 minutes. Transfer the mixture to a food processor and puree. Transfer to a shallow pan and let cool completely, about 15 minutes in the refrigerator or 5 minutes in the freezer.