Heat oven to 350 degrees. Meanwhile, melt butter in large Dutch oven over medium-high heat until foaming subsides, about 1 minute. Add onion and sauté until it turns soft and translucent about 4 minutes. Add garlic and sauté until fragrant, about 30 seconds. Add half and half, milk, thyme, bay leaves, salt, pepper, and potatoes and bring to simmer.

Cover pot and maintain a light simmer, and cook until potatoes are almost tender, about 15 minutes. Remove bay leaf.

Transfer potato mixture to 3-quart baking dish and sprinkle with cheese. Bake until the cream has thickened and is bubbling around sides and the top is golden brown, about 20 minutes. Cool for 5 minutes before serving.