Line an 8"x8" pan with unbleached parchment paper in both directions, to easily remove the marshmallows once they are set.
Dust the bottom of the pan with half of the arrowroot flour. Set pan aside.
Add 1/2 cup of the purified water to a mixing bowl (if you're using an upright stand mixer use the bowl that comes with it), then sprinkle the gelatin over the water. Let this "bloom" while you make the syrup mixture.
In a medium-size sauce pan, add 1/2 cup purified water, honey, maple syrup, vanilla extract and sea salt. Bring the mixture to a boil over medium-high heat. Stir constantly to keep it from scorching or overflowing.
Turn the heat down and simmer until mixture reaches 240 degrees on the candy thermometer, which will take about 10-15 minutes, depending on your stove. Remove from heat.
With the mixer on low, SLOWLY pour the hot syrup mixture in a narrow stream down the side of the mixing bowl into the gelatin. You should pour so slowly that this should take 1–2 minutes to complete. (If you are using a hand mixer, have someone else slowly drizzle the syrup while you use the mixer.)
Turn the mixer to high and continue beating until the mixture becomes thick, glossy and fluffy—about 10-15 minutes.
Quickly transfer marshmallow fluff to the lined and floured pan. Use a spatula to evenly spread the mixture and smooth out the top.
Dust the top of the marshmallow fluff with the remaining arrowroot flour.
Let the marshmallows sit at room temperature to set for at least 8 hours, or overnight.
When marshmallows are set, remove them from the pan by lifting out the parchment paper. Carefully peel the parchment paper from the sides of the marshmallows and use a large knife to cut them into 1- or 2-inch squares.
Dust with additional arrowroot flour as needed to keep them from sticking together.
Store marshmallows in a sealed container for 3-4 days.
Homemade marshmallows melt and toast much faster than store-bought ones with chemical stabilizers! Use great caution when toasting over open flame.