Combine the gelatin and initial measure of milk in the bowl of a stand mixer. If using powdered gelatin allow to bloom fully with the milk as the liquid. Separately, combine all remaining ingredients except the egg whites, and heat to a boil. In this case it pays to watch the pot, because the milk will boil over.
Pour this mixture over the gelatin in the bowl of a stand mixer. Using a paddle attachment, beat for 25 seconds at low speed to incorporate. Raise the speed to high and whip until a thick, stringy looking foam stands tall in the mixer, about 4 minutes.
Gently beat the egg whites to start incorporating air and add them to your marshmallow. The marshmallow will break but reconstitute shortly. Beat an additional 2 minutes and then pour into a prepared mold and let set completely.
Cut as desired, lace with powdered sugar, and enjoy.
If you are piping marshmallows, beat an additional 4 minutes to ensure have taken in the most air and cooled enough to hold their shape when piped. Pipe onto a prepared surface and let rest completely.