Cooking the sweet potatoes in a slow cooker frees up space on the stove if you're cooking a big holiday dinner—plus you can serve it straight from the crock if you'd like.
Peel sweet potatoes and slice 1/4 inch thick. Place in a 6-quart or larger slow cooker. Add orange zest, orange juice, 2 tablespoons each butter and brown sugar, vanilla, cinnamon, 1/2 teaspoon salt, 1/4 teaspoon pepper and nutmeg. Stir to combine. Cover and cook until the sweet potatoes are tender, about 3 hours on High or 61/2 hours on Low. Mash with a potato masher until smooth.
Heat the remaining 1 tablespoon butter in a medium nonstick skillet over medium heat until foaming. Add pecans, bourbon, cayenne and the remaining 1 tablespoon brown sugar and 1/4 teaspoon each salt and pepper. Cook, stirring, for 2 minutes. Remove from heat.
Transfer the sweet potatoes to a serving dish, if desired, and sprinkle with the pecans.