Preheat oven to 425°. Whisk spices and salt in a small bowl. Slit vanilla bean lengthwise, then scrape out seeds; add them to a large bowl. (Bury vanilla pod in sugar for future baking, if you like.) To seeds, add pumpkin, eggs, and sugar and whisk to blend, using a sideways stirring motion so as not to beat in air (pie will be smoother). Whisk in spice mix, then whisk in cream and crème fraîche. Strain into another bowl.
Pour custard into a 10-in. quiche pan or a 9-in. pie pan. Bake 15 minutes, then lower heat to 350° (325° if pan is glass) and bake until center is almost set, 15 to 20 minutes.
Cool on a rack 2 hours, then sprinkle with pecans. Serve with a spoon and dollop with whipped cream if you like.
MAKE AHEAD: Up to 2 days, chilled.