Preheat your oven to 350°F (175°C). Melt the unsalted butter and let it cool slightly. In a mixing bowl, combine graham cracker crumbs with melted butter and a pinch of salt. Press the crumb mixture into the bottom of a springform pan. Bake for 8–10 minutes until golden, then cool completely.

Prepare a water bath by wrapping the outside of the springform pan with heavy-duty aluminum foil. Place it inside a larger roasting pan, set aside until cheesecake batter is ready.

In a bowl, beat softened cream cheese until smooth. Gradually add sugar, then sour cream, lemon juice, vanilla, and salt. Mix until incorporated. Slowly add eggs, one at a time, mixing just until combined.

Pour cheesecake batter over the cooled crust. Place this pan in the roasting pan, pouring boiling water into the roasting pan until it reaches about 1/3 up the sides of the springform pan. Bake at 325°F (165°C) for 60–75 minutes, until edges are set and center jiggles slightly.

After baking, turn off the oven and leave the cheesecake inside for an additional hour. Transfer to a wire rack to cool completely. Chill in the refrigerator for at least 6 hours, preferably overnight.

For the pastry cream, whisk egg yolks and sugar in a saucepan until light. Whisk cornstarch and flour in a bowl. Gradually temper warm milk into egg mixture, then back to the saucepan. Cook over medium heat until thickened. Stir in butter and cool completely.

Once pastry cream is chilled, spread it over the top of the cheesecake. Just before serving, sprinkle granulated sugar on top and caramelize using a kitchen torch until bubbly and golden.