To make the gelee: Put the grapes, lemon juice, sugar and water in a medium-sized pot and set over medium heat. Simmer for 20 minutes until grapes are tender and skins have completely discolored. Using a potato masher squash the grapes to release all of the juices. Do not puree in a blender otherwise your gelee will be cloudy and pick up parts of the skin. Pour the mixture through a sieve over a large measuring cup or bowl with a spout and use the back of a ladle to firmly press the pulp - this will extract as much juice and flavor as possible. This should yield about 3 cups (24 ounces) of liquid. If it is more or less add water or pour out some of the liquid, otherwise the gelatine ratio will be off. Slowly whisk in the gelatin powder, making sure you continue to whisk until it is all fully incorporated. Divide the grape jelly mixture into 4 to 6 glasses depending on the size of your glasses. Gently agitate to remove any surface bubbles then refrigerate for 3 to 4 hours, or overnight, until set.
To make the salad: In a small pot, over medium heat, add the sugar, cold water, sliced lemon and ginger. Bring to a simmer, then add in the basil and shut off the heat to allow the mixture to steep, 20 minutes. Cut the grapes in half through the middle and add to a large mixing bowl. Dress the grapes with a little of the syrup and toss to combine. Discard the basil and reserve the extra syrup.
To make the whipped cream: Using a balloon whisk, whip the cream, sugar and vanilla until soft peaks form. Fold the ginger into the whipped cream but reserve a few pieces for garnish.
To assemble the dish: When the gelee is set, remove it from the refrigerator and top each glass with a spoonful of the grape salad and a quenelle of the ginger whipped cream. Garnish with basil buds and some slivers of ginger. Drizzle each glass with some of the reserved lemon-ginger syrup and serve.