a quantity of fruit or vegetables (good choices include: sweet potatoes, corn, apples, broccoli, carrots, peaches)
Skin your fruit or vegetables if necessary. If the vegetable is something like an apple or potato, cut it up into small pieces.
Either place in a steamer and steam until soft or place in a pot with just covered with water and boil until soft. Drain water off and puree in a food processor or mash by hand.