1. Place the brisket in a Dutch oven or heavy skillet in which it will fit compactly. Pour boiling water over it barely to cover. Return to a boil and reduce the heat. Spoon off all the grease and scum.
2. Add the remaining ingredients and cover lightly. Simmer 3 to 4 hours until the meat is tender.
3. To make Horseradish Sauce, Melt the butter in a saucepan, add the flour and stir with a wire whisk until blended. Add the boiling broth all at once, stirring vigorously with the whisk until the mixture is smooth and thickened. Season with horseradish. (Makes about 1-1/2 cups.)