Beat egg whites and cream of tartar in a medium mixing bowl with an electric mixer on high speed until foamy. Beat in sugar, 1 tbsp. at a time; add vanilla. Beat until stiff and glossy. Drop by 1/4 cupfuls onto 2 parchment-lined baking sheets. Using the back of a spoon, shape into bird's nest-shaped bowls. Bake in a preheated 275° oven 1 hr.; turn off oven and leave meringues in oven with door closed (1 ½ hrs.). Cool completely at room temperature. Fill meringues with Kowalski's Lemon Curd and/or Sweetened Whipped Cream; top with fresh berries and Balsamic Berry Sauce or your favorite dessert sauce.