Add chicken stock to a large pot and bring to a boil over high heat. Add farro and boil until the grains are softened and chewy, about 7 minutes. If you feel that there isn’t enough liquid to finish cooking the farro, go ahead and add a cup or so of water. Once farro is cooked, drain and set aside. In a large skillet over medium high heat, add 2 tablespoons butter. Once the butter is melted, add the chard, salt and pepper. Saute until chard is wilted, about 5 minutes. Stir in cooked farro, last 2 tablespoons of butter, mustard and mustard seeds. Stir together until well combined.