Place the diced sweet potatoes in the slow cooker.
In a separate bowl, mix together the chicken broth, melted butter, brown sugar, cinnamon, nutmeg, salt, and black pepper until well combined.
Pour the mixture over the sweet potatoes in the slow cooker, ensuring they are evenly coated.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the sweet potatoes are tender.
If using, sprinkle mini marshmallows and chopped pecans on top during the last 30 minutes of cooking. Cover and let them melt slightly.
Once done, stir gently to combine and serve warm.