Nope. Just be sure the water covers the egg--half inch? And VERY occasionally
it will pop, so cover with a saucer or plastic lid. I've only had one pop. You don't puncture the yolk. It is really really a GREAT way to have a perfectly poached egg.
And the shape of the cup, makes a very nice form. I do it in a 1 cup measuring cup usually.
And I have misspoke--it isn't Thomas Keller's recipe--Bon Appetit and Genius Kitchen, I guess.
Here are the "exact" directions.
When I worked the line at Jasper White's Summer Shack in Cambridge, Massachusetts, we made poached eggs to order in the microwave. The technique yields perfect silky, firm whites and runny, warm yolks every time.
To replicate this restaurant trick at home, fill a 1-cup microwaveable bowl or teacup with 1/2 cup water. Gently crack an egg into the water, making sure it's completely submerged. Cover with a saucer and microwave on high for about 1 minute, or until the white is set but the yolk is still runny. Use a slotted spoon to transfer the egg to a plate.