Preheat oven to 350 degrees. Grease a shallow casserole dish with butter or cooking spray.
In a medium saucepan, melt butter over medium heat.
Add shallots to pan and cook 2-3 minutes until soft. Add garlic and cook until fragrant, about 1 more minute.
Add heavy cream, thyme, salt and pepper to saucepan. Stir to combine. Simmer for 5 minutes. Turn off heat and set aside.
Evenly distribute the sweet potato rounds in your casserole dish. If your casserole dish is larger, you can add more potatoes. Ideally the potatoes should be about 3 layers deep.
Slowly pour cream mixture evenly across the potatoes, taking care to get into all areas around the slices. Optional - top with 1/2 cup of shredded cheese. I used Irish Cheddar.
Bake for 35-40 minutes or until the potatoes are tender.
