Preheat your oven to 325°F (160°C). Place 6 (4-ounce) ramekins into a large roasting pan or baking dish. Bring a kettle of water to a boil for the water bath.

In a medium saucepan, combine the heavy cream, whole milk, diced apple, cinnamon stick, star anise, whole cloves, freshly grated nutmeg, and the vanilla bean (if using vanilla extract, add it later). Heat the mixture over medium heat until it just begins to simmer around the edges. Do not boil. Remove from heat, cover, and let steep for 20-30 minutes to allow the flavors to infuse.

In a large mixing bowl, whisk together the egg yolks, granulated sugar, and salt until pale yellow and slightly thickened. This should take about 2-3 minutes.

Strain the steeped cream mixture through a fine-mesh sieve directly into the egg yolk mixture, pressing on the apple pieces and spices to extract maximum flavor. Discard the solids. If you are using vanilla extract, stir it in now. Whisk gently until fully combined, being careful not to create too many bubbles.

Pour the custard mixture evenly into the prepared ramekins. Carefully transfer the roasting pan with the ramekins to the oven. Pour the boiling water from the kettle into the roasting pan until it reaches halfway up the sides of the ramekins. This creates a water bath (bain-marie) which ensures even cooking and prevents cracking.

Bake for 40-50 minutes, or until the edges are set but the centers still have a slight jiggle when gently shaken. Cooking time may vary depending on your oven and ramekin size. Be careful not to overbake, as this can make the custard grainy.

Carefully remove the roasting pan from the oven. Using tongs, carefully lift the ramekins out of the water bath and place them on a wire rack to cool completely at room temperature. Once cooled, cover each ramekin with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until thoroughly chilled and firm.

Just before serving, uncover the chilled crème brûlées. Sprinkle about 1 tablespoon of granulated sugar evenly over the top of each custard. Use a kitchen torch to caramelize the sugar until it melts, bubbles, and turns a rich amber color. Move the torch continuously to prevent burning. If you don't have a torch, you can place the ramekins under a preheated broiler for 1-2 minutes, watching constantly to avoid burning.

Serve immediately and enjoy the satisfying crack of the caramelized sugar.