Step 1

Heat a large pot or Dutch oven over medium-high heat. Add butter and onion and let cook for 5-6 minutes, stirring often.  Add garlic and cook for 30 seconds. Meanwhile, peel and slice potatoes.

Step 2

Add heavy cream, milk, thyme, salt, pepper, and potatoes. Cover with a lid and reduce heat to low to keep a mild simmer. Parboil potatoes for about 15 minutes, or until the potatoes are almost tender. Preheat oven to 350 degrees.

Step 3

Transfer potato mixture to 3-quart baking dish or gratin dish. Sprinkle with cheddar cheese. If you want the cheese to be melted throughout, carefully mix the cheese into the potatoes.

Step 4

Bake until bubbling around the edges and cheese is melted and golden, about 20-25 minutes. Let cool for 5 minutes before serving.