Line a 9X12 baking dish with parchment paper and set aside.

In a small bowl combine powdered sugar and cornstarch to make the marshmallow powder. Set aside.

Add the gelatin to a medium sized bowl. Add ½ cup of water and set aside for about 10 minutes.

In a pot combine sugar, corn syrup, and ½ cup water. Warm over medium heat until sugar granules are melted.

Pour sugar mixture into the gelatin and use an electric mixer to slowly start mixing. As the mixture begins to stiffen you can speed it up. Scrape down sides as some will edge up. Mix until thick peaks begin to form. This may take up to 15 minutes. Add in vanilla extract and carefully stir in.

Add to the parchment lined baking dish and evenly flatten. Sprinkle about a quarter of the marshmallow powder you made earlier on top.

Cover with saran wrap. Let sit on counter overnight.

Once marshmallows have rested grab a large cutting board. Remove saran wrap and carefully flip baking dish onto cutting board. Remove parchment paper.

Add about half of remaining marshmallow powder to what is now the top.

Spray a large knife or rocking pizza blade with nonstick spray. Use it to create desired sized marshmallow cubes. Sprinkle the remaining marshmallow powder on the newly exposed sides.

Store in an air-tight container.