Preheat the oven to 200°C (390°F). Place the butter, thyme, salt and pepper in a small bowl and stir to combine. Place half of the butter mixture under the skin of the chicken and place in a baking dish with the sage, garlic and potatoes. Roast for 15 minutes, turn the chicken and roast for a further 15 minutes or until golden and cooked through. Melt the remaining butter mixture and pour over the chicken and potatoes to serve.Serves 4.