The classic technique is to crack the egg, then pass the yolk from one half-shell to the other, letting the whites drip and slither out into a bowl below. This became practica non grata when salmonella contamination of shells became a widespread problem; antibacterial enzymes in egg whites would ordinarily keep the yolk clean, but not when the yolk contacts the shell edge as it does in this technique. So various clever kitchen doodads were invented, and sold at a substantial profit, for the separating of eggs.

Since then, the salmonella problem in U.S. poultry has gotten worse. It is now endemic, internally, in laying hens, which means that salmonella can be deposited directly into the yolk of an egg before the shell is even laid down. This is why it is no longer advisable to eat raw cookie dough, and why I don't even contemplate making any recipe with undercooked egg yolks in it. But there is a silver lining: The safety measures that address potential salmonella in the yolk also address potential salmonella transferred from the shell. Which is to say, letting the shell touch the yolk is now no more risky than anything else you might be doing with that yolk. And that means a frugal dude in a crowded apartment need not worry about getting and storing an egg separator. Shells will work just fine.