add the unflavored gelatin to 1/2 cup of the water to a stand mixer mixing bowl. The water will moisten the gelatin causing it to swell up and thicken. This is called "blooming".
In a medium saucepan add the water, sugar, corn syrup, and salt. Stir to mix and then turn the heat up to high. Cover the pan and bring the mixture to a boil. (takes about 4 minutes)
Once the mixture is boiling, remove the lid, and clip a candy thermometer to the edge of the kettle. Monitor the temperature, and remove the kettle from the heat when the syrup mixture reached exactly 240 degrees. (about 8 minutes)
Turn your stand mixer on med-low and slowly pour the hot syrup mixture down the side of the bowl into the gelatin. Continue pouring until all the syrup is added to the bowl. Turn the mixer up to high speed and mix on high for 13 - 15 minutes.
Add the vanilla and mix in during the last 1 minute of beating. The marshmallow mixture will be lukewarm and the consistency of thick marshmallow fluff.
Cut the graham cracker bottoms with a round 3-inch biscuit cutter. each graham cracker will make two mallomar bottoms.
Add the pastry tip to the pastry bag and fill the Pasty bag with as much of the marshmallow mixture as will fit into the bag.
Pipe the marshmallow onto the graham cracker rounds to form a mound of marshmallow on each round. Refill bag as needed until all of the marshmallow mixture is gone. Let the marshmallow crackers sit until the marshmallow has dried enough to not stick when touched. Usually for about 30 minutes.