In a mixing bowl, sprinkle gelatin over 1/2 cup of cold water. Let it sit for about 10 minutes to bloom.

In a saucepan over medium heat, combine granulated sugar, light corn syrup, salt, and the remaining 1/2 cup of cold water.

Stir the mixture until the sugar dissolves completely.

Insert a candy thermometer into the saucepan and allow the syrup to reach 240°F (115°C) without stirring.

Once the sugar syrup reaches the desired temperature, carefully pour it into the bowl with the gelatin mixture.

Using a hand or stand mixer, beat the mixture on high speed until it becomes thick and fluffy, which usually takes about 10-15 minutes.

Add vanilla extract during the last minute of mixing.

While the mixture is whipping, prepare a 9x13 inch (23x33 centimeters) baking pan by lining it with parchment paper and lightly greasing it.

Once the mixture is thick and fluffy, quickly pour it into the prepared pan, using a spatula to spread it evenly.

Let the marshmallow mixture sit at room temperature for at least 4 hours, or preferably overnight, until it firms up completely.

In a small bowl, combine powdered sugar and cornstarch to create a coating mixture.

Sprinkle the coating mixture generously over the top of the set marshmallow slab.

Use a sharp knife or kitchen shears to cut the marshmallows into squares or desired shapes.

Toss each marshmallow square in the remaining coating mixture to prevent sticking.

Your homemade marshmallows are now ready to be enjoyed! Serve them as they are or use them in your favorite recipes.

Store any leftovers in an airtight container at room temperature for up to 2 weeks.