Coat a square baking dish with powdered sugar

In a large mixing bowl, add ½ cup cold water and sprinkle with gelatin

Set aside while gelatin softens

Place a candy thermometer on the side of a medium saucepan, add ½ cup water, sugar, corn syrup, and salt

Bring to a gentle boil over medium heat and cook until thermometer reads 240 degrees F (softball)

Turn the mixer on low and slowly drizzle in hot sugar mixture

When all sugar has been added, turn the mixer to high and beat for 10 minutes or until stiff peaks form

When the marshmallows have reached stiff peaks and the bowl is cooled to room temperature, add the vanilla and mix

Transfer mixture into prepared baking pan and work quickly to spread evenly. The marshmallows will be very sticky, you can wet your fingers to spread if necessary.

Sprinkle with additional powdered sugar

Let marshmallows set out overnight

To cut, add a general amount of powdered sugar to a large cookie sheet or cutting board

Loosen marshmallows slightly from the edge of the pan using a sharp knife

Remove marshmallows and place on board with the powdered sugar

Sprinkle marshmallows with additional powdered sugar

Cut into 1-inch squares and toss to coat with additional powdered sugar, if desired

Store in an airtight container for 5-7 days