Position racks in the upper and lower thirds of the oven and preheat to 350 degrees . Draw six 2-by-3-1/2-inch rectangles, spaced about 2 inches apart, on each of 2 sheets of parchment paper. Turn the parchment face down on 2 large cookie sheets. Using an electric mixer, beat the egg whites at medium speed until foamy, about 2 minutes. Beat in the salt and cream of tartar and then beat in the sugar, 1 tablespoon at a time, until stiff peaks form. Fold in the vanilla until barely incorporated.
Using a small offset spatula, spread the batter on the parchment. Transfer to the oven, turn off the heat and let stand for 1 hour. Transfer to racks to cool completely.
Peel the meringues off the parchment and set aside. Place 1 parchment-lined cookie sheet and a medium stainless-steel bowl in the freezer for at least 10 minutes. In the frozen bowl, combine the ice cream and sorbet with a rubber spatula. Working quickly, spread 1/2 cup of the ice cream mixture onto the flat side of 6 meringues. Cover with the remaining meringues and freeze on the frozen cookie sheet for 30 minutes.
Meanwhile, in a small saucepan, warm the jam and 2 tablespoons water. Stir in the berries and heat through. Spoon the berry sauce onto each of 6 dessert plates and place a meringue sandwich in the middle.