In a medium bowl, whisk together the heavy cream, melted butter, garlic, thyme, salt, and pepper until fully combined.
Layer 1/3 of the sliced potatoes in the bottom of your slow cooker. Pour 1/3 of the cream mixture over the potatoes, then sprinkle 1/3 of the cheddar and Parmesan cheese on top.
Repeat the layering process two more times, ending with the cheese on top.
Cover the slow cooker with the lid and cook:
High: 3–4 hours
Low: 5–6 hours
or until the potatoes are tender and easily pierced with a fork.
Optional: Garnish with freshly chopped chives before serving.