Liberally grease a 13 x 9 baking dish and use with powdered sugar, Set aside
In a stand mixer bowl with whisk attachment, add 1/2 of the hibiscus syrup then sprinkle all of the gelatin and let stand to soften.
I a median saucepan with a heavy bottom, combine the remaining hibiscus syrup, sugar, corn syrup and salt and cook over medium to low heat stirring with a wooden spoon until al of the sugar has dissolved.
Then turn up the heat a little and going to a boil without stirring until it reaches 240F on a cane thermometer about 10-15 minutes depending on your heat level, pot etc.
Remove from heat and carefully pour over the gelatin mixture in the stand mixer bowl. Site until all of the gelatin has dissolved.
Begin to beat this mixture carefully working your way up to high speed. The mixture will still be fairly hot. Beat on high for 8-10 minutes until glossy and thick. There should be a nice ribbon flow when you lift up the beater.
In a separate bowl, a copper one of you’ve got it, beat the egg whites/ reconstituted egg white powder by hand until your form sift peaks.
Add the egg whites and vanilla to the marshmallow mixture and beat until just combined.
Quickly pour the marshmallow mixture into the prepared baking dish and spread into an even layer. Dust the surface with more powdered sugar and let set for 7 hours or overnight.
When you are ready to cut the marshmallows, liberally dust a cutting board with powdered sugar and turn out the marshmallows onto the board. You may need to run a knife mourned the edges to help it release. Use a greased knife or pizza cutter to cut into squares. Spray cookie cutters with cooking spray if using. Roll the marshmallows into more powdered sugar and shake off excess. Eat em up.