2.
Place a marshmallow on top of one half of the doughnut, and place it in the microwave. Melt the marshmallow at 10 to 15-second intervals until the it expands and melts (probably two 15-second intervals, or about 30 seconds total, but microwaves may vary).
3.
Remove the doughnut half and marshmallow from the microwave and swirl it around a little to shape the marshmallow like an egg white, you can also carefully use a spoon to help flatten the marshmallow if it's not flat enough. A tiny bit of oil on the bottom of the spoon will keep it from sticking.