combine water, sugar, corn syrup and salt in sauce pan and, over medium head, bring to bubbly stage. Raise the heat to med-high and boil without stirring until the temperature reaches 250 degrees F
pour into stand mixer with whisk attachment and cool to 212 degrees F
whisk in the gelatin on low until it is melty and incorporated, then raise the power to high whip it until white, fluffy and pulling away from edges of the mixing bowl- around 10 minutes
smear into a greased 8x8" pan (I find a silicon pan works like magic for ths recipe.) The marshmallows firm up after 2 hours in the fridge, or 24 hours at room temperature
after they are firm, cut using scissors into cubes, coating with powdered sugar as needed to keep them from being too sticky (I drop them into the powdered sugar bowl and just toss around as I cut them)
Notes
to make tie-dye marshmallows, separate into separate bowls and add food coloring, then add to the prepared 8x8'' pan and swirl with a knife to combine all the colors OR add food coloring drops at last 15 seconds of mixing try not to over mix.