Spray slow cooker with non-stick spray.
Place potato slices in slow cooker. Season well with salt and pepper.
In a small saucepan, melt butter over medium heat. Whisk in flour to create a paste. Season with garlic powder and black pepper. Slowly whisk in milk. Continue to cook and stir over medium heat until mixture is smooth and starting to thicken. Remove from heat. Stir in cheese until melted. Stir in heavy cream.
Pour cheese sauce mixture over potatoes.
Cover and cook on HIGH 3-4 hours.
Garnish with chopped chives just before serving.