Put the gelatin in your stand mixer with the whisk attachment and add ½ cup of the water. Have this on stand by for later.

In a small pan combine the remaining ½ cup water, white sugar, corn syrup and salt. Cook over a medium heat until the mixture reaches 240 degrees F, about 7 to 8 minutes. Once the mixture reaches this temperature remove it from the heat immediately.

Next turn the mixer on low speed and, while running, slowly pour the sugar syrup down the side of the bowl into the gelatin mixture. Once it's all combined, continue mixing on high speed until it becomes very thick and is lukewarm, about 12 to 15 minutes. Add the vanilla and food colouring at the end, adding enough to food colouring to achieve the colour you like.

Mix the powdered sugar and cornstarch in a small bowl. Lightly spray a 13 by 9-inch metal baking pan with nonstick cooking spray and add the sugar and cornstarch mixture. Carefully the pan around to completely coat it.

Next pour the marshmallows into the prepared pan, using a lightly oiled spatula to spread it evenly. Dust the top of the marshmallows as well with enough of the remaining sugar and cornstarch mixture to lightly cover. Reserve the rest for later. Let the marshmallows sit uncovered overnight.

Turn the marshmallows out onto a cutting board and cut into 1-inch squares using a pizza wheel dusted with the icing sugar mixture. After cutting lightly dust each marshmallow with the remaining mixture. Store in an airtight container for up to 3 weeks.