Brown the butter: Melt the butter in a skillet or small saucepan over medium heat. Swirl or stir the butter with a wooden spoon as it starts to foam and sputter. When the butter begins to turn golden brown and smells nutty, about 1 minute. To the brown butter, add the apples, sage leaves, salt, and pepper. Cook, stirring, until the apples are just tender, about 4 minutes. Serve with pork or chicken.