I have used cream of tartar here in the meringue but you don't have to. It acts as a stabiliser in recipes that require whipped egg whites, such as meringue, angel sponges and soufflé. When whipped, egg whites can swell up to eight times their initial volume and the acidity of cream of tartar helps egg whites achieve their full volume potential, and stabilises them by helping hold in water and air. Just make a normal meringue without it if you don't have it.
If you don't have raspberry sorbet you could use a fruit ice cream as a contrast and add a raspberry coulis to it to add an element of sour. You just need some combination of fruit and ice cream - maybe even add some frozen raspberries to the vanilla ice cream?
I have no fresh raspberries at the moment so will make this will frozen raspberries for the sorbet and I have some strawberries so decorate with strawberries and raspberry coulis.
Recipe adapted from The Great British Bake Off, Get Baking