In a 2- to 3-quart pan over medium-high heat, frequently stir whipping cream, sugar, orange peel, nutmeg, and salt just until steaming, about 4 minutes.
Meanwhile, scrub sweet potatoes, peel, and slice crosswise very thinly. Spread slices in an even layer in a buttered shallow 3-quart casserole (9 by 13 in.). Pour hot cream mixture evenly over sweet potatoes.
Bake in a 350° oven for 30 minutes. Dipping liquid from casserole edge, spoon over sweet potatoes to moisten, then sprinkle evenly with pecans. Return to oven and bake until potatoes are well browned and tender when pierced, about 30 minutes longer.