Line an 8- or 9-inch square dish with parchment paper or aluminum foil. Lightly grease with melted butter or coconut oil. Set aside.
Pour about half the cold water into the bowl of a stand mixer (with the paddle attachment) or a large mixing bowl. Sprinkle the gelatin over the water and allow to bloom while preparing the syrup.
In a small saucepan, add the remaining water, monk fruit, xylitol, and salt. Clip a candy thermometer to the side of the pan then bring the mixture to a boil (no stirring necessary). Allow to boil until the temperature reaches exactly 240° F (soft ball stage).
Turn the stand mixer onto low or start beating with hand mixer on lowest setting. SLOWLY add the very hot syrup mixture into the softened gelatin, being very careful not to let it splatter (it's HOT and also very sticky and messy).
Turn the mixer to medium speed (if splattering occurs, turn it down until it gets a little thicker then turn back up).
Mix for 5 minutes then add vegetable glycerin and flavorings. Mix for an additional 5 minutes or until the mixture is fairly thick and white.
Pour into the prepared dish and spread around (you can use your hand to spread it by greasing your hand with a bit of butter or coconut oil to keep it from sticking).
Allow to dry, uncovered, at room temperature for 4-6 hours.
Cut the dried marshmallows into the desired sized squares. Or use cookie cutters to cut them.
If you want a different flavor of marshmallow, omit the marshmallow and vanilla flavorings and add the flavorings as indicated in the blog post. Or make up your own flavor combos!