Place the drained sauerkraut, mayonnaise, thousand island, 1 cup of Swiss cheese, and the diced corn beef in a large bowl. Gently mix until combined.
Spread the mixture into a greased 8x8 inch baking dish or 8 inch pie dish. Top with the remaining 1 cup of Swiss cheese.
Bake for 20–25 minutes, or until the dip is browned and bubbly. Serve with rye crackers or toasted rye bread for dipping.
Notes
Be sure to drain the sauerkraut very well, otherwise the dip will end up watery. Can't find rye crackers? Use toasted rye cocktail bread or your favorite crackers for scooping instead.