Gather your ingredients.
Add gelatin and ½ cup cold water to mixer bowl
In heavy-bottomed pan pour remaining water, corn syrup, and granulated sugar.
Cook at medium heat until temperature reaches 240 degrees.
This will take 7-8 minutes. Once temperature is reached, remove from heat.
Turn mixer with gelatin and water on low, and slowly pour in heated mixture to combine.
Once all of the heated mixture is added turn on high and beat for 12-15 minutes, until mixture forms thick peaks.
Add vanilla extract, mix well, turn off mixer.
While mixer is running, prepare the pans.
First, spray pans with non-stick spray then combine powdered sugar and cornstarch in bowl. Sprinkle pans with mixture, coating the bottom and sides.
Save the remaining mixture to use on marshmallows.
Pour marshmallow mixtures from mixer into your prepared pans.
Use a greased spatula to smooth it around the bottom and edges of pan.
Let cool at room temperature for 4-6 hours.
Once completely cooled and set, cut into 1-inch squares with powdered sugar covered paring knife (to prevent sticking).
Sprinkle cut marshmallows with remaining powdered sugar/cornstarch mixture to prevent sticking.