How to Make Homemade Marshmallows

1. Line 9x9-inch pan with parchment paper/plastic wrap or foil. Lightly oil it and set aside.
2. In the bowl of an electric mixer, sprinkle gelatin over 1/2 cup cold water. Let bloom for about 15 minutes.
3. Meanwhile, combine sugar, salt corn syrup and 1/2 cup water in a small saucepan, whisking only until the sugar is dissolved. Bring the mixture to a boil. Boil until a candy thermometer reads 240°F (115°C). Do not stir while mixture is cooking.
4. Turn on your mixer to low-medium speed, add vanilla extract and whisk bloomed gelatin for 30 seconds, carefully pour the hot sugar syrup down the side of the bowl into the gelatin. When all the syrup has been added, increase the speed to high and whip for about 10 minutes (at this stage you can add food coloring if desired), until thick and fluffy.
5. Immediately pour into prepared pan, and spread it evenly with an oiled offset spatula. Let sit for at least 6 hours at room temperature.
6. Make the dusting mixture: Combine the powdered sugar and cornstarch in a bowl.
7. Sprinkle generously the top of the cured marshmallows with some of the dusting mixture, then sprinkle a cutting surface very generously with dusting mixture. Flip the block of marshmallows out onto you’re the working surface. Oil and dust a big sharp knife with dusting mixture and cut the marshmallow into squares.  
8. Toss each square in dusting mixture so all the sides are evenly coated.

Notes:

• Keep the marshmallows in an airtight container at room temperature for up to 2 weeks.
• Can I replace corn syrup? The main reason why corn syrup is added is to prevent crystallization of the sugar syrup. I personally have never tried replacing corn syrup. But, some recipes online say you can substitute corn syrup with agave syrup or maple syrup.