Prepare corned beef with mustard sauce by first boiling a 5- to 6-pound corned beef brisket in a kettle filled with water. Add 12 peppercorns and one large bay leaf to the kettle and simmer for about 3.5 hours while preparing the mustard sauce.
Ingredients in mustard sauce include 1/4 cup of butter, 1/4 cup of flour, 3 tablespoons of dry mustard, 2 tablespoons of brown sugar and 1 1/2 teaspoons of salt. It also uses a dash of ground red pepper, 2 cups of milk, 2 large beaten eggs and 1/4 cup of cider vinegar.
Melt the butter in a saucepan over low heat. Slowly add the flour to the pan and stir it continuously. Sprinkle in the dry mustard, 2 tablespoons of the brown sugar, salt and the red pepper and stir the ingredients together. Cook the mixture for two minutes. Pour the milk into the pan and cook the ingredients until the sauce begins to boil.
Pour a small amount of the liquid from the pan into the bowl holding the beaten eggs, and then immediately pour the mixture into the saucepan. Cook the sauce for one minute. Remove the pan from the heat and add the vinegar.
Remove the brisket from the kettle, sprinkle it with 1/4 cup of the brown sugar and broil it in the oven until the sugar bubbles. Serve it with the mustard sauce.