Homemade Marshmallows

Grease a 9-inch square baking pan with nonstick spray or a thin layer of oil. For extra ease when removing the marshmallows, dust the pan with a mix of sifted confectioners’ sugar and cornstarch.
Pour 1/2 cup of water into the bowl of an electric mixer. Evenly sprinkle 2 envelopes of unflavored gelatin over the water and allow it to bloom for about 10 minutes.
In a medium saucepan, combine 1/2 cup water, sugar, corn syrup, and salt. Heat over medium, stirring until sugar dissolves. Stop stirring and boil until a thermometer registers 240°F. Remove from heat.
With the mixer on low, slowly pour the hot syrup into the gelatin along the bowl's side.
Once fully added, increase to high and whip for 3-5 minutes until thick and fluffy, nearly tripling in volume. It should form thick ribbons when you lift the whisk out of it. Add vanilla and mix for another minute.
Transfer the marshmallow mixture into the prepared pan, smoothing the top with a greased spatula or oiled hands (it will be hot and sticky). Let it set at room temperature for at least 4 hours until firm. To serve, dust a cutting board with confectioners’ sugar and cornstarch.
Turn the marshmallow slab onto the board and use a lightly oiled knife to cut it into squares. Coat the pieces in additional dusting powder to avoid sticking, then place them in an airtight container for storage.