Smear the butter all over the 6-quart insert of your slow cooker. Put a third of the sweet potato rounds into your slow cooker and sprinkle on 2/3 teaspoon of chipotle chile powder and a 1/3 teaspoon of kosher salt. Add 1/3 of the shredded cheese. Repeat the layers until you have run out of ingredients. Pour the heavy cream evenly over the top.
Cover, and cook on low for 5 hours, or on high for about 2 hours.