Prepare the sugar syrup
Bloom the gelatin
The protein in the gelatin is key to getting the mixture to whip up once you beat the sugar syrup in. Simply substituting a vegetable gelatin, which is mostly starch, will not work.
Add syrup to gelatin
This is when having both a stand mixer and an electric hand mixer is really useful. While the marshmallow fluff is fluffing up, beat the egg whites in a separate bowl if you are using them.
Beat the egg whites (optional)
If you are using egg whites, beat them until stiff peaks form. You can also beat reconstituted powdered egg whites. Just don’t use pasteurized egg whites from the carton; they’ll never form the peaks that you need.
Add the beaten egg whites to the marshmallow fluff
Spread into a prepared pan and allow to set
Turn out and cut
Use cookie cutters, scissors, or a sharp chef’s knife to cut the marshmallow into pieces. If you use a knife, press the knife down into the marshmallow – it will bounce back. Don’t saw back and forth.