Line your baking sheet with parchment paper.
Get out your electric mixer and the bowl of your stand mixer. Set it up with the whisk attachment. In the bowl of an electric mixer add in the cold water. Then sprinkle gelatin on top of the cold water.
Let the gelatin sit and soak for 10 minutes.
In a small saucepan, combine sugar, corn syrup, and 1/4 cup water and heat over medium heat. Bring the mixture to a boil and let it boil for 1 minute.
Once the sugar syrup mixture is done, pour the boiling sugar syrup into the gelatin mixture in your electric mixer. Turn the mixter speed to high speed and carefully add in the salt.
Allow the mixture to beat on high speed for 12 minutes.
After 12 minutes add in the vanilla extract and turn th mixere to medium-low speed and mix just to incorporate it into the mixture.
Use a spatula to spread a little bit of cooking oil onto the parchment paper and you will want to add some to the side of the pan you are using. This will prevent the marshmallow mixture from sticking to it.
Rub the rubber spatula again with oil and pour the marshmallow mixture onto the sheet pan lined with parchment paper and spread evenly. Scrap any of the mixture out of the mixing bowl.
Get another piece of parchment paper and spread oil on one side, then place the oil side down on top of the marshmallow mixture.
Let the marshmallow mixture sit for at least 2 hours. You want the marshmallows to firm up, depending on the temperature in your house it might take a little longer for the marshmallows to set.
Remove the homemade marshmallow slab from the pan.
Dredge (which means to cover the whole thing) the marshmallow slab with confectioners’ sugar. You only want a light coating of confectioners’ sugar on the top of them.
Cut marshmallows into equal pieces with a pizza wheel or a large sharp knife, you can make them any size you want to.
Dredge each piece of marshmallow in powdered sugar again lightly.