To make sweet potato puree, prepare the sweet potatoes in one of these two ways:
Bake 1 pound (455g) of sweet potatoes, with skins on, at 375°F (190°C) until soft, about 1 ½ hours. Cool the potatoes slightly, peel, and press through a fine-mesh sieve. Or, peel the potatoes and boil them until soft, 20 to 30 minutes, then press through a fine-mesh sieve. Baking is slightly more flavorful, but boiling is much quicker.