- In a saucepan, heat the milk and vanilla. Add the chocolate, stir to melt, then whisk before serving.
- Line a 33 x 23-cm (13 x 9-inch) dish with plastic wrap and oil with your fingers. It is important to oil the dish completely.
- In a bowl, combine the sugar and water. Add the vanilla.
- In another bowl, sprinkle the gelatin on the cold water and let bloom for 2 to 3 minutes, then melt completely in the microwave or bain-marie. Add to the sugar mixture.
- Beat with an electric mixer for about 10 minutes or until the mixture has the texture of a soft meringue. Spread into the pan and let set overnight.
- Cut the marshmallows into cubes and roll in the powdered sugar and cornstarch mixture.
To keep the rest of the marshmallow, leave it uncovered for 24 hours, then store it in an airtight container. It will keep for several days.