Melt 2 tablespoons butter in large saucepan over medium-high heat. Add garlic, onion, and thyme and cook for 2 minutes or until tender. Add rice and stir to combine. Add chicken stock and bring to a boil. Reduce heat, cover and simmer for 45 minutes or until rice is tender but not over cooked. Melt remaining butter in a medium skillet over medium-high heat. Add mushrooms and cook for 1 minute or until tender. Stir mushrooms, salt, pepper, and half-and-half into soup and cook until heated through. Serve at once.