From WikiPilipinas: The Hip 'n Free Philippine Encyclopedia
Puto is a slightly sweet steamed cake made out of rice flour (galapong). Galapong is created by letting rice soak overnight and ferment, then grinding it while it is still wet. Yeast is normally added to the mixture as well. Sometimes toppings like salted egg or cheese are added. They may be made round, oval, or in rectangualr sheets. Nearly every Philippine town has its own unique variety of puto. Some of the most popular are:
Putong Polo, from the town of Polo, Bulacan. These are about one inch in diameter and may be white or reddish brown. The color of the latter comes from brown sugar.
Puto Binan, a light brown puto, which is the specialty of Binan, Laguna.
Puto Bumbong, named after the bamboo tube in which it is steamed. It is unusual among puto, coming in a long thin shape and a purple color. The elongated shape results from the method of cooking while its color comes from the violet pirurutong rice it is made of. It is served with grated coconut and brown sugar. Along with bibingka, it is often served outside churches around Christmastime.
Puto Pao, which like Chinese siopao has a meat filling.
Fernandez, Doreen G. "Foodscape: Rice Cakes of Remembrance." In FOOD Magazine, February 1996.