Prepare sandwiches by dividing corned beef and cheese evenly among buns.
Add 1 Tbsp. sauerkraut (drained) to each sandwich.
Place sandwiches in a 9x13 inch pan or a rimmed baking sheet.
In a small saucepan, combine remaining ingredients. Bring to a boil over medium-high heat.
Remove from heat and pour over sandwiches.
Cover with foil and refrigerate sandwiches overnight. (*Note: this step can be eliminated if necessary)
Uncover sandwiches and bake at 350 degrees for 20-30 minutes.
Serve with Thousand Island dressing if desired.