Remove corned beef from the package, place in a large pan or dutch oven cover with water. Add the little seasoning package, turn heat to high, bring to a boil. Turn the heat down so the water stays at simmer, but do not allow it to boil. Cover with a lid and cook "low and slow" for 2-3 hours. The corned beef should be very tender and almost falling apart. Remove from water carefully and cool to room temperature.
Build the Open Faced Reubens:
Toast rye bread in the toaster or oven. Spread with Dijon mustard. Cut bread slices in half and shingle (4 half slices per reuben) in a baking pan. Slice the cooked corned beef thin and stack it on the rye bread, (cover the bread). Top with sauerkraut and slices of Swiss cheese. Bake in a 400-degree oven until golden brown.
Serve with Russian dressing.
Combine mayonnaise, chili sauce, horseradish, lemon juice, dijon mustard and grated onion in a bowl. Mix well.