Preheat the oven to 250°. In a large bowl, using an electric mixer on medium speed, beat the egg whites until soft peaks form. With the mixer running, gradually add 1 3/4 cups sugar, the cornstarch, and lemon juice. Beat on high until a stiff, glossy meringue forms, about 10 minutes. On a baking sheet lined with parchment paper, spread the meringue into a 2-inch-high rectangle. Dollop with 1/4 cup jam. Using a silicone spatula, fold in the jam to create swirls (do not overmix). Bake the meringue until crisp, about 1 hour and 20 minutes. Turn off the oven and prop open the door. Let the meringue cool in the oven for 30 minutes. Transfer to a platter.
In a large saucepan, cook the blueberries and 1/4 cup jam over medium-high heat, stirring often, until a thick sauce forms, about 10 minutes. Let cool.
In another large bowl, using an electric mixer on medium speed, beat the cream and the remaining 1/4 cup sugar until slightly firm peaks form. Spread the whipped cream over the meringue. Dollop with the remaining jam. Fold in the jam to create swirls. Top with the blueberry sauce and lemon zest. Dust with confectioners’ sugar.