I have used this method a number of times since I first read it. The timing varies by microwave oven and by egg, because every egg is not the same size. I like the yolks to be runny and the whites completely cooked, which is a perfection that hasn't quite happened, but close enough that I continue to prepare eggs this way. The shape of the mug makes a difference too. I like the result better in a mug that doesn't have completely vertical sides, but is rounded at the bottom to a narrower base. Puncturing the yolk is advisable. If you don't puncture the yolk, I've had only a small hole explode out of the yolk, but it propelled the entire egg out of the mug. That was the first and only time I forgot to cover the mug. The yolk doesn't run out as the egg cooks when you puncture it before cooking. I use the tip of a sharp knife or the tines of a fork. Use a saucer or small dessert or salad dish as a cover, particularly if you don't puncture the yolk. You can hear the egg hit the lid if/when it explodes. The entire yolk doesn't explode, only a small hole will be visible and the yolk itself appears intact, but the force against the cover rocks it. Use a slotted spoon to remove the egg from the mug.
