Spray slow cooker with nonstick cooking spray. Add peeled and diced sweet potatoes to the slow cooker and fill with water until potatoes are fully submerged.

Cover and cook on high for 4 hours.

When finished cooking, drain water from the slow cooker, keeping sweet potatoes in the slow cooker.

Using an electric hand mixer or potato masher, mash potatoes until smooth.

Add milk, butter, brown sugar, salt, cinnamon and nutmeg; mix until well combined.