Mix the cornstarch and powdered sugar. Dust a 9 inch baking pan with half of the powdered sugar mix.
In the bowl of a mixer, mix the agar agar in 1/2 cup water. In the meantime, Boil the remaining water, agave, and sugar until it reaches the soft ball stage (240 degrees). You can use a candy thermometer, or take a little of the syrup and drop it in a glass of water. If it forms a soft ball, it's there.
Whisk the agar in the mixer at low speed. Drizzle in the hot syrup until incorporated. Add the rest of the ingredients. Turn up the speed and continue whipping until frothy like a meringue.
Spread the mix evenly in the dusted pan. Dust the top with more powdered sugar mix. Refrigerate or set aside at least an hour until the marshmallows set up.
Once set, Cut the marshmallows with a knife dipped in water. Then spread them out on a sheet pan and put in an oven set on warm (150 to 170 degrees). Let them sit in oven about 10 minutes to dry them out a bit and create a bit of a crust. This step is optional. But, it helps with the consistency of the marshmallows. when done, Toss them in more powdered sugar.
