Increase the heat to medium, add the apples, tossing well, and cook until they start to brown. Cover, reduce the heat to low and cook until the rice is tender, about 20 minutes. Toast walnuts in a 350°F (175°C) oven for 5 to 7 minutes. Preheat the oven to 375°F. In a large bowl, combine olive oil, orange zest, orange juice, vinegar, salt, pepper and nutmeg; mix well. Chop coarsely and set aside. Add the rice and thyme. Add the onion and cook until softened, about 3 to 5 minutes. Cook for 1 to 2 minutes, then add the chicken stock, apple juice, butter, vinegar and some salt and bring to a simmer. In a Dutch oven or 12-inch diameter skillet with 2-inch straight sides, melt the butter over medium-high heat.