With cooking spray, grease the bowl of a slow cooker. Stack half of the potatoes in the slow cooker.
In a small saucepan, add the butter and place over medium heat. Add the flour and whisk until combined. Continue to cook for 3 minutes, stirring constantly. Add the milk, while vigorously whisking. Bring to a simmer and cook, stirring constantly, until thick, about 7 minutes. Add the Hidden Valley® Original Ranch® Seasoning, Salad Dressing & Recipe Mix Packet, thyme, nutmeg, salt, pepper and cheese, and stir to combine and to melt the cheese. Pour half of the sauce over half of the potatoes, but do not stir.
Layer the remaining potatoes on top. Pour remaining sauce on. Place paper towels over the bowl of the slow cooker and place the lid on top. Cook on low for 3–4 hours.
For safe meat preparation, reference the USDA website.