Wash some grapes and take them all off the stalks. Place them in the freezer for at least a few hours. (I just leave some in there to have a few when I want them)
Either serve the grapes straight from the freezer whole. The centres go quite slushy so taste like sorbet.
Or to make it even more like sorbet us a hand blender to blend them up (you may need to pop it back in the freezer after)