Creating the perfect Japanese Sweet Potato Crème Brûlée involves a few straightforward steps. Follow these carefully for the best results:

1. Prepare the Sweet Potatoes: Preheat the oven to 400°F (200°C). Wrap the sweet potatoes in aluminum foil and bake for 45 minutes, or until tender. Once baked, let them cool before peeling.
2. Blend the Sweet Potatoes: In a mixing bowl, mash the peeled sweet potatoes until smooth. Set aside.
3. Heat the Cream: In a saucepan, combine the heavy cream and half of the granulated sugar over medium heat. Stir occasionally until the sugar dissolves and the mixture just begins to simmer. Remove from the heat.
4. Combine Egg Yolks: In another bowl, whisk together the egg yolks, remaining sugar, vanilla extract, and salt until well combined.
5. Mix Sweet Potato and Cream: Slowly pour the heated cream mixture into the egg yolk mixture while whisking continuously to temper the eggs. Ensure it is well blended.
6. Add Sweet Potato: Gently fold in the mashed sweet potatoes until smooth and uniform in color.
7. Pour into Ramekins: Divide the mixture into individual ramekins, filling them about three-quarters full.
8. Prepare the Water Bath: Place the ramekins in a larger baking dish. Carefully pour hot water into the baking dish until it comes halfway up the sides of the ramekins.
9. Bake: Bake in the preheated oven for about 30-35 minutes, or until the edges are set but the center is still slightly wobbly.
10. Cool and Chill: Remove the ramekins from the water bath and let them cool to room temperature. Once cooled, cover them with plastic wrap and refrigerate for at least 2 hours (or overnight) to set.
11. Caramelize the Top: Before serving, sprinkle a thin layer of granulated sugar over the chilled custard. Using a kitchen torch, carefully caramelize the sugar until it forms a golden-brown crust. Allow it to cool for a minute.

With these steps, your Japanese Sweet Potato Crème Brûlée will be ready to wow your guests or satisfy your sweet cravings.