Preheat the oven to 325°F. Prepare the mascarpone cream: In the bowl of a stand mixer fitted with the paddle attachment, combine the mascarpone with the powdered sugar. Gradually add the heavy cream in a thin stream and continue to mix until the filling is smooth and thick. Set aside.
Prepare the meringue: Combine the whites, vanilla, lemon juice, and salt in the bowl of a stand mixer fitted with a whisk attachment (* make sure that your bowl is very clean as the eggs will not whip properly if there is any fat). Begin whipping the egg whites. When they start to look foamy gradually add the granulated sugar about 1 tbsp at a time. Continue whipping until the whites have formed a shiny thick meringue-like shaving cream. Remove the bowl from the stand mixer and fold in the cornstarch. Spread onto a quarter sheet tray or a 9”x13” pan that has been greased and lined with parchment paper. Bake for about 30 minutes or until the meringue has puffed, sunken a bit, and turned a golden color. Let cool completely. Run a knife along the edge of the pan to release the meringue and then flip it out onto a clean sheet of parchment paper. Fill with a layer of mascarpone filling and then about 1/2 c of lemon curd. Beginning on the short end and using the parchment paper as an aid, roll the meringue up and place it on a serving dish with the seam side down. Dust with powdered sugar and serve immediately with extra lemon curd (or wrap and chill for up to one day).