Bring potatoes, stock, 2 cups water, the thyme, and garlic to a low boil in a large saucepan over medium heat. Cook until potatoes are tender, 10 to 12 minutes.
Preheat oven to 375 degrees. Put pan juices into a roasting pan; heat in oven 10 minutes. Drain potatoes; pat dry. Add potatoes to pan, and cook, turning halfway through, until golden brown, about 30 minutes. Season with salt and pepper.