Scrub the sweet potatoes and pierce each one several times with a fork. Leave whole or halve large potatoes so they cook evenly.
Place the potatoes in a single layer in the slow cooker. It’s okay if they’re nestled; just try for even distribution.
Whisk together brown sugar, cinnamon, nutmeg, orange juice, maple syrup (if using), and salt. Scatter butter pieces over the potatoes and pour the glaze on top.
Cover and cook on LOW for 5–7 hours or HIGH for 2.5–3.5 hours, until potatoes are tender when pierced with a knife.
Carefully remove potatoes and pour cooking juices into a small saucepan. Simmer 3–5 minutes until slightly thickened, then spoon over the potatoes.
Sprinkle with flaky sea salt and chopped thyme or parsley. Serve warm.
Notes
Cook time varies by slow cooker and potato size—check doneness after 5 hours on LOW.
For a crisp finish, broil the glazed potatoes 3–4 minutes after slow-cooking—watch closely.
Store leftovers in an airtight container up to 3 days; reheat in a 350°F oven with additional glaze.