Soak gelatine in cold water. Wash the grapes and, except for a few for decoration, halve and core them. Heat wine and apple juice and season with sugar and lemon juice.
Squeeze out the gelatine, dissolve in it and let it cool down. Pour a little liquid into a glass bowl, let it solidify, then add grapes. Repeat the process until everything is in layers.
Leave to set in the refrigerator for about 3 hours. Stir 3 tablespoons of milk, sauce powder and 2 tablespoons of sugar until smooth. Heat the remaining milk, stir in the sauce powder and bring to the boil, then chill.
Dip the rest of the grapes briefly in water and roll in the remaining sugar. Decorate jelly with sugared grapes.