Eggs – How to beat one or two egg yolks

If you want soft and moist, you need egg yolks. Their emulsifier and fat content makes dough pliable, soft and smooth, and retains moisture.

Egg whites dry out a dough. This is sometimes desirable, e.g. in pate a choux. Eclairs made with whole eggs often have wet planes in the middle, resulting in an underbaked impression. If you remove some yolks from the dough and use a mixture of whole eggs and egg whites, you get a firmer, drier dough. But in many cases, people want softer, moister end products, and in such cases, recipes which increase the ratio of egg yolks to egg whites (by using more yolks than whole eggs, or yolks only) will give you a better result.

Double-yolked eggs are the result of an anomaly in the egg generation process in the hen.

They can happen in any breed of hen, on any feed. It is a result of two ova being generated at the same time, and then encapsulated in a single shell. According to My Pet Chicken, it happens more often with younger hens.

I am not aware of any process to intentionally foster double yolked eggs, but that doesn't mean such a thing doesn't exist.

They are safe to eat, although they may be visually startling.