Prepare the sweet potatoes: Preheat your oven to 400°F (200°C). Pierce the sweet potatoes a few times with a fork, then roast them on a baking sheet for 45-60 minutes, or until soft. Alternatively, microwave for 8-10 minutes. Let cool slightly, peel, and mash the flesh until smooth.

1. Make the custard: In a medium saucepan, combine the heavy cream, whole milk, cinnamon, nutmeg, ginger, and salt. Split the vanilla bean lengthwise, scrape out the seeds, and add both seeds and pod to the saucepan (or use vanilla extract). Heat until just simmering, then remove from heat to let the vanilla infuse.
2. In a large bowl, whisk the egg yolks and sugar until smooth. Gradually pour the hot cream mixture into the egg yolks while whisking constantly. Strain through a fine mesh sieve to remove any curdled bits and the vanilla pod.
3. Combine with sweet potato: Whisk the mashed sweet potato into the custard until smooth and fully incorporated.
4. Pour into ramekins: Pour the custard into 6-8 ramekins, filling about 3/4 full. Place the ramekins in a large baking dish and add hot water until it reaches halfway up the sides.
5. Bake the crème brûlée: Bake for 40-45 minutes, or until the edges are set and the center is slightly jiggly. Cool in the oven for 1 hour with the door ajar, then refrigerate for 2-3 hours or overnight.
6. Caramelize the sugar: Just before serving, sprinkle an even layer of sugar over the top of each crème brûlée. Use a kitchen torch to caramelize until golden and crispy. Alternatively, broil under a preheated broiler for 1-2 minutes, watching carefully.
7. Serve: Let sit for a minute to cool the caramelized sugar, then serve and enjoy!