1. Preheat the oven to 350°F (conventional, no fan). Bring all cheesecake ingredients to room temperature.
2. Crush the graham crackers into fine crumbs and blend them with melted butter. Line a 9-inch springform pan with parchment paper, firmly pressing the crust mixture into the bottom and slightly up the sides. Bake for 8-10 minutes, then cool completely.
3. Lower the oven temperature to 325°F.
4. Wrap the springform pan in two large sheets of aluminum foil to prevent water leaks during the water bath.
5. In a stand mixer, beat cream cheese, sugar, vanilla essence, and salt on medium speed until smooth. Add the eggs one at a time on low speed, mixing well. Then mix in heavy cream, sour cream, cornstarch, and lemon juice until combined.
6. Pour the cheesecake batter over the cooled crust and tap the pan gently to remove air bubbles. Place the pan in a water bath and bake for about 80 minutes, until the edges are firm but the center is slightly jiggly.
7. Remove from oven and cool to room temperature for 2 hours before refrigerating overnight.
8. For the lemon curd, combine lemon juice, eggs, sugar, cornstarch, and salt in a saucepan. Cook over low heat, stirring constantly until the mixture thickens. Stir in butter until melted, strain through a sieve to remove lumps, and chill.
9. For the Swiss meringue, whisk egg whites, sugar, and cream of tartar over simmering water until the mixture reaches 150°F. Then beat the mixture until stiff peaks form.
10. Spread chilled lemon curd evenly over the cheesecake. Top with the Swiss meringue and lightly toast using a kitchen torch for a golden finish.