1. Prepare the meringue. Preheat the oven to 250 degreesF. Line 2 baking sheets with parchment paper. With the dull end of a knife, mark 2 rectangles on one piece of parchment paper and 1 rectangle on the second piece of parchment paper. Each should measure 4-by-13 inches. Spray the paper lightly with vegetable cooking spray.
2. In a large bowl, use an electric mixer on low speed to beat egg whites and cream of tartar until frothy. Increase speed to medium-high and beat until soft peaks form. With mixer on medium, slowly add sugar and beat until whites are stiff. Add lemon zest and mix just to blend.
3. Scoop dollops of meringue mixture over the three marked rectangles and use a spatula to spread it to the shape. The meringues should be 3/4 inch thick. Bake until the meringues are crisp and dry, about 90 minutes. Turn off the oven: let the meringues rest in the oven for 1 hour, then remove.
4. While meringues bake, prepare the filling. Dissolve cornstarch in 1/2 cup of the water. Set aside. Whisk egg yolks, remaining 1/2 cup water, sugar, and lemon juice together in a medium saucepan. Cook over medium-low heat until the sugar dissolves, whisking slowly but constantly. Stir in cornstarch mixture, increase the heat to medium-high, and bring to a boil, stirring the mixture constantly. Cook until thickened, about 30 to 60 seconds. Remove from heat. Strain into a bowl through a sieve. Stir in 1/2 tsp. of the lemon zest. Press plastic wrap onto the filling and poke a few holes in the plastic wrap with a sharp knife to let steam escape. Refrigerate until cold and thick, at least 2 hours or up to 2 days.
5. When meringues are ready, prepare the whipped topping. In a medium bowl, use an electric mixer on medium-high to whip cream, mascarpone, and confectioners' sugar until light and fluffy. Add vanilla, 2 Tbsp. of the lemon filling, and the remaining 1 tsp. lemon zest. Beat a few seconds until blended; peaks should be firm. Transfer to a large resealable plastic bag and seal. Snip a half inch off one corner.
6. Peel the parchment from the meringues. Slide one meringue onto a platter. Spread half of the filling over the meringue. Place 1/2 cup of the chopped mango along the center of the length of the rectangle. Pipe 1/3 of the whipped topping over the mango and layer with a second meringue. Repeat with remaining filling and chopped mangoes and another 1/3 of the topping. Layer third meringue on top.
7. Pipe the remaining whipped topping over the top meringue. Arrange the mango slices in a decorative pattern over the top. Cover and refrigerate at least 1 hour but no more than 2 hours. To serve, cut with a serrated knife.
Source: Hannaford fresh Magazine, May - June 2013