Put gelatine and 150 ml cold water into a small pot and mix. Leave to swell for about 10 minutes. In the meantime mix cornflour and 2 tbsp. icing sugar. Oil a square form with a lifting base (approx. 20 x 20 cm) and generously dust with a good half of the icing sugar-starch mix.
Sift 250 g icing sugar into a bowl. Heat gelatine while stirring and bring to the boil briefly. Immediately pour the boiled hot gelatine into the icing sugar while stirring.
Whisk the icing sugar and gelatine mixture with the whisks of the mixer for 4-5 minutes until firm and foamy, until peaks form.
Stir 1-2 tablespoons of jam or 1 tablespoon of food colouring into the marshmallow mixture or fold it in with a spoon in streaks.
Pour the mixture immediately into the prepared mould. It is best to spread the mixture with an oiled dough scraper. Leave to dry for approx. 1 hour at room temperature.
Remove the marshmallow plate from the mould. Cut the mixture into 2-3 cm cubes with a lightly oiled knife on a board dusted with the rest of the icing sugar-starch mix. Alternatively you can also use a lightly oiled cookie cutter.