How to make Marshmallows

Homemade Marshmallow recipe:
2/3 cup powdered sugar
1/3 cup cornstarch
1 cup cold water
2.5 Tbsp un-flavored gelatin
2/3 cup light corn syrup
2 cups granulated sugar
1/4 tsp salt
2 tsp vanilla
_________________
Make a foil sling for a 13x9 pan with pieces of foil 13 inches wide and 9 inches wide.
Smoothly cover the pan with foil, overhanging the edges of the pan. Spray with cooking spray. Whisk powdered sugar and cornstarch together in a small bowl and set aside.
Pour ½ cup water into the bowl of a stand mixer. Sprinkle gelatin over the water and let stand until the gelatin becomes firm, about 15 minutes. Meanwhile, combine remaining ½ cup water and corn syrup in medium saucepan.
Pour granulated sugar and salt into center of pan (do not let the sugar hit the pan sides). Bring to a boil over medium-high heat, and cook, gently swirling pan, until sugar has dissolved completely and mixture registers 240 degrees, 6 to 8 minutes.
Turn mixer speed to low and carefully stream hot syrup into gelatin mixture. Try to avoid getting the syrup on the sides of the bowl.
Gradually increase speed to high and whip until mixture is thick and stiff, 10 to 12 minutes, scraping down bowl as needed. Add vanilla and mix until incorporated, about 15 seconds.
Working quickly, scrape mixture evenly into prepared pan using greased rubber spatula, smoothing the top. Sift 2 Tbsp powdered sugar mixture over pan.
Cover and let sit overnight at room temperature until firm. Lightly dust cutting board with powdered sugar mixture and lightly coat chef’s knife with cooking spray.
Turn marshmallow slab onto a cutting board, peel off foil and sift 2 Tbsp powdered sugar over the slab.
Cut into 1-inch wide strips and then cut crosswise into 1-inch squares.
Working with 3 or 4 marshmallows at a time, toss in a bowl with remaining powdered sugar mixture, then toss in a mesh strainer to remove extra powder.
Store in airtight containers for up to 2 weeks.