1 can (20 ounces) reduced-sugar cherry pie filling
Place egg whites in a large bowl; let stand at room temperature for 30 minutes. Add cream of tartar and vanilla; beat on medium speed until soft peaks form. Gradually beat in sugar, 1 tablespoon at a time, on high until stiff glossy peaks form and sugar is dissolved.
Spread onto the bottom and up the sides of a greased 13-in. x 9-in. baking dish. Bake at 275° for 1 hour; turn oven off (do not open door). Let meringue cool in oven for at least 8 hours or overnight. Just before serving, spread with whipped topping and top with pie filling.