Butter all sides of a 9x13 pan and set aside. In a small bowl, whisk together powdered sugar and cornstarch. Dust all sides of the buttered pan with the sugar mixture. A sifter works great for this! Set remaining mixture aside.

To a stand mixer add 1/2 cup water. Then, sprinkle gelatin across the top. Let that sit to bloom, or absorb some of the water, while you do the next step.

To a small saucepan add: ½ cup of water, sugar, corn syrup , and salt. Whisk it together over medium heat. Put on the lid and let heat up for about 4 minutes until it comes to a boil.

Remove the lid and cook, without stirring, until the mixture comes to a temperature of 240 degrees Fahrenheit. This will take about 5-7 minutes.

Carefully take the hot syrup mixture and pour it down the sides of the stand mixer bowl while the mixer runs on low speed. After it comes together, turn up your mixer speed to medium.

Let it run for about 10 minutes until the mixture fluffs up. While it is mixing you can tap off any extra powdered sugar in your pan. Towards the end, add in vanilla extract, and then let it mix in for a minute more.

Use a buttered spatula to transfer the marshmallow fluff to the pan and smooth it down evenly. I like to butter my hands next so that I can get it a little smoother and flatter.

Dust the tops with more of the powdered sugar mixture and smooth it out so that just a light layer covers the entire surface. Cover remaining mixture and set aside.

Cover the pan and set it aside for a minimum of 3 hours to firm up. Do not try to cut them right away because they don’t quite have the structure yet.

Use a buttered knife to cut into your desired size. Dust all sides with the remaining powdered sugar mixture. Store in an airtight container.