In a small saucepan, combine half the water and the agar-agar powder. Bring to a simmer and stir until the agar dissolves completely.

In a large saucepan, combine the remaining water, sugar, and corn syrup. Cook over medium heat until the sugar dissolves.

Once both mixtures are ready, combine them, stirring constantly until thick and fluffy or using a whisk attachment on a stand mixer. Add in the vanilla extract for flavor.

Pour the mixture into a pan dusted with powdered sugar and cornstarch. Let it set for a few hours or overnight.

Cut the marshmallows into squares and dust them with powdered sugar to prevent sticking. Enjoy your homemade, vegan marshmallows!