- Line an 8-inch (20 cm) square baking pan with plastic wrap and oil lightly.
- In a small saucepan, combine the water and vanilla. Sprinkle the gelatin over the water and let bloom for 5 minutes. Add the sugar and heat gently, stirring until the sugar and gelatin have dissolved. Let cool for 5 minutes.
- Pour into a bowl and add the corn syrup. Beat with an electric mixer until soft peaks form, about 10 to 12 minutes. Spread into the prepared pan and refrigerate for 2 hours or until the marshmallow has set.
- In a bowl, whisk together the cornstarch and icing sugar.
- Sprinkle a work surface and a knife with some of the cornstarch mixture. Unmould the marshmallow. Cut into 25 large cubes and coat with the starch mixture. Shake to remove any excess.
- If desired, caramelize the marshmallows using a small culinary torch or around a campfire. Serve immediately.
Replace the water with a fruit purée of your choice for marshmallows with different colours and flavours.
Starch and sugar-coated marshmallows (not caramelized) will keep for 1 to 2 weeks at room temperature in an airtight container.