Combine all ingredients, adjust according to taste. Refrigerate any unused dressing.
For the sandwich...
Spread Russian dressing on one side of each bread slice, then layer corned beef, Swiss cheese, and sauerkraut in triple-decker fashion.
Melt butter in large skillet, pan grill sandwiches until nicely browned, using a bacon press or similar to weigh it down. Add additional butter then turn sandwiches browning other side.