птичье молоко (literally: "bird's milk")
In Russian fairy tales, "bird's milk" is a luxury so fantastic it doesn't even exist.
Тебе что, птичьего молока надо? Птичьего молока не хватает?
An egg in your beer?
Example 2: When I was quite young, my Mom's expression was "Whadaya want; an egg in your beer?" when I'd been given something, but was whining for something else to go with it (SF)
This dates back as far as the WWII when both food items were scarce and having either was considered extremely lucky. 'Egg in your beer' is normally used to stop somebody complaining about a situation you think to be favourable.
Pelated vocabulary: