Use an electric or stand mixer, set to high speed, to beat together the egg whites. Add dry vanilla. Whip until the mixture forms soft, fluffy white peaks.
3 egg whites,, ¼ tsp dry vanilla
Meanwhile, on the stove, bring to a boil in a medium-sized pot 1 cup of water and agar-agar. Whisk powdered sugar into the pot, and boil for exactly 6 minutes.
1 cup water, 2 tsp agar-agar, 4 cups powdered sugar
Take off the heat and add the agar mixture to the egg whites with the mixer on low speed. Mix for another 3 minutes.
Shape or pipe the marshmallow mixture onto two large baking sheets. Shape the marshmallows into any shape you want. I used a pastry bag with a decorating tip. If you're worried about stickiness, try dusting the baking sheet with a little powdered sugar.
Let marshmallows stand at room temperature for at least 30 minutes. For faster results put it in the refrigerator. Enjoy!
Notes
Boil the agar-agar for exactly 6 minutes for the perfect texture. Boiling longer will affect the texture.