Place the Corned Beef Brisket (3 pound) in a pot and cover with water. Add the seasoning pack and bring it to a boil. Reduce the heat to a simmer and cover the pot. Cook for 3 hours. Remove from the pot, once tender, and keep warm.
Mix the Mayonnaise (1/2 cup), Ketchup (5 tablespoon), Dill Pickle Relish (1/4 cup), Onion (1 tablespoon), Worcestershire Sauce (2 teaspoon), Yellow Mustard (1 teaspoon), and Salt (1 pinch) in a bowl and whisk together. Set aside.
Heat a pan to 375 degrees F (190 degrees C).
Heat the Sauerkraut (1 cup) in a small pan and keep warm.
Slice the corned beef thinly and portion the corned beef slices 6 ounces per sandwich - about 8 slices each.
Brush the Butter (4 tablespoon) on all sides of the Rye Bread (8 slice) slices and grill each side in a hot skillet -until brown.
Spoon the dressing on the open-faced sides of all 8 slices of grilled bread and spread evenly.
Layer each side of all 8 slices of dressed bread with 2 slices of Swiss Cheese (1 pound).
On only one side of the sandwich, top the Swiss cheese with 2 tablespoons of warm sauerkraut, and then top the sauerkraut with the slices of corned beef. Each sandwich should have 6 to 8 slices of hand-cut corned beef.
Place the toasted rye bread slice, the one with only Swiss cheese, on top of the corned beef Swiss cheese side down. Press the sandwich lightly until the cheese is fully melted.
Cut in half or on the diagonal and enjoy!