Here's the recipe:
Separate the yolk from as any egg whites as you are making. In a chilled metal bowl, whisk the whites until stiff peaks form. Mix in whatever you want.
Spoon the whites into even piles on a baking sheet and create a well in the center of each pile with the back of the spoon.
Bake at 450F for 3 minutes.
Put a yolk in each well, bake another 3 minutes at 450F.