For the cheese sauce, in a medium mixing bowl, whisk together heavy cream, cream of chicken soup, 1/2 cup of both the cheddar cheese and gruyere cheese, dried minced onion, garlic powder, salt and pepper.
Lightly grease a crockpot with nonstick cooking spray or butter. Add 1/2 of the potatoes in a single layer. Lightly season with salt and pepper. Evenly drizzle on half of the cheese sauce. Repeat these 2 layers.
Add paper towels to the top of the crockpot, stretching it beyond both ends so that it doesn't drape down and touch the potatoes when covered with the lid.
HIGH cook steps: Cook 3 hours. Insert a knife to check doneness. If not done, cook an additional 30-60 minutes. LOW cook steps: Cook 5 hours. Insert a knife to check doneness. If not done, cook an additional 30-60 minutes.
Once they're tender, turn off the crockpot. Gently blot any excess grease from the top with a paper towel, if needed. Add the remaining cheeses in an even layer, recover with the lid, and allow the mixture to set up for 30 minutes.
If desired, garnish with fresh parsley before serving.