Steam cook the sweet potatoes until tender. Transfer to a mixing bowl, add honey, molasses, vanilla extract, cinnamon, and nutmeg. Mix and mash with an electric beater/mixer until smooth. Set aside.
Preheat oven to 350°F. In a large bowl, mix (do not whip) together egg yolks and gradually add 1/2 cup sugar until the egg turns lighter in color. Heat the cream in a saucepan and bring it to a boil, then slowly pour into the egg mixture while stirring constantly. Add salt and 2 tbs vanilla extract. Pour custard mixture into the sweet potatoes and mix until it turns a darker color with lumpiness.
Grease ramekins or ovenproof custard cups with butter. Place ramekins in a roasting pan and fill each ramekin 3/4 full with the custard and sweet potato mixture. Add hot water around the ramekins to reach about three-fourth of the way up the sides to create a bain marie.
Bake in the oven for 35 - 40 minutes, remove ramikens from water bath and let them cool at room temperature then refrigerate at least 2 hours before serving.
The custards may be stored covered in the refrigerator for up to 3 days. Before serving allow the creme brulees to warm up a little at room temperature. Sprinkle evenly a thin layer of turbinado sugar or white sugar on the surface of each ramiken. Using a blow torch, melt the sugar to form a crispy sugar crust on top of each ramekin.
Crème Brûlée can be served with fruits of the season or with whipped cream on top.