Preheat your oven to 350°F (175°C). Combine the graham cracker crumbs, granulated sugar, and melted butter. Press the mixture into the bottom of a springform pan and bake for 10 minutes until golden brown. Allow it to cool completely.

In a saucepan, pour the heavy cream and add the vanilla bean or extract. Heat over medium until it simmers, then remove from heat. In a separate bowl, whisk the egg yolks, granulated sugar, and cornstarch until pale and thick. Slowly pour the warm cream into the egg mixture, whisking continuously to prevent curdling.

Pour the custard filling over the cooled crust. Create a water bath by placing the springform pan inside a larger baking dish filled with hot water. Bake at 300°F (150°C) for 50-60 minutes, until the custard is set around the edges.

Remove the cake from the water bath and let it cool at room temperature for about 2 hours. Cover with plastic wrap and refrigerate for at least 4 hours or overnight.

Before serving, sprinkle a thin layer of granulated sugar on top. Using a kitchen torch, caramelize the sugar until it turns golden brown. If not using a torch, place it under the broiler for a few seconds.

Allow the caramelized sugar topping to cool. Slice the cake and serve immediately, garnishing with fresh berries or whipped cream.