How many penguin baby eggs does one mother produce at one time?

I believe each penguin couple only produces one egg at one time. The mother and father must protect their egg by resting it on their feet up under their belly to keep it warm. When one parent goes to feed, the other parent sits on the egg. The fishing parent can be gone a long time. When that parent returns, they get their feet close as they face each other, and the other parent takes the egg so the starving parent can then go fish and feed. They do the same thing after the baby hatches, so the baby is always kept warm.