How to Make It
MAKE THE CRUST Preheat the oven to 350°. In a medium bowl, stir the graham cracker crumbs with the melted butter, sugar and salt until the crumbs are evenly moistened. Press the crumbs into the bottom and up the sides of a 9-inch springform pan. Bake until lightly browned and set, about 10 minutes. Transfer to a wire rack and let cool completely. Wrap the outside of the pan with foil.
MAKE THE CHEESECAKE Reduce the oven temperature to 300°. In a standing electric mixer fitted with a paddle attachment, beat the cream cheese with the mascarpone and lemon zest at low speed until smooth, about 4 minutes. Add the sugar, 1/4 cup at a time, beating well after each addition and scraping down the side of the bowl occasionally. Beat in the salt and then the eggs one at a time, scraping the bowl after each addition. At low speed, beat in the vanilla with the lemon curd until no streaks of curd remain. Pour the cheesecake batter into the pan and place the pan in the center of a large roasting pan. Place the roasting pan in the oven, and carefully pour in enough hot water until it reaches halfway up the side of the springform pan. Bake the cheesecake for 1 hour and 30 minutes, until it is set around the edges and slightly jiggly in the center. Turn off the oven and let the cheesecake stand in the cooling oven for 1 hour.
Remove the cheesecake from the water bath and discard the foil. Transfer to a wire rack and let cool room temperature for 1 hour. Run a sharp, thin-bladed knife around the cake and remove the ring. Refrigerate the cake for 3 hours, until chilled completely.
MAKE THE MERINGUE Preheat the oven to 325°. In a medium saucepan, combine the sugar and water and bring to a boil. Cook over moderate heat until the syrup reaches 243° on a candy thermometer, about 6 minutes.
Meanwhile, in the bowl of a stand mixer fitted with the whisk, beat the egg whites with the cream of tartar at medium speed until soft peaks form, about 4 minutes. With the machine on, slowly drizzle in the hot syrup and beat the meringue at medium-high speed until stiff and glossy, about 6 minutes longer. Scoop the meringue onto the cheesecake, spreading and swirling it decoratively; make sure the meringue covers the filling completely and touches the crust all around.
Return the cheesecake to the middle rack of the oven and bake for 10 minutes. Turn on the broiler; broil the meringue 6 inches from the heat until golden brown in spots, about 3 minutes. (Alternatively, you can use a blow torch to brown the meringue.) Let cool slightly before serving.