Preheat oven to 350 degrees F.
In a bowl, combine Thousand Island dressing, yogurt, and sauerkraut, stirring to combine.
Spray 9x13" baking pan with cooking spray.
Place 5 cups of the bread on the bottom of the pan.
Spread 1/2 of the Thousand Island dressing/sauerkraut mixture over bread.
Top with corned beef and 1 cup of cheese.
Spread remaining Thousand Island dressing/sauerkraut mixture over the cheese.
Evenly distribute remaining bread on top, pressing into the dressing mixture so it sticks.
Top with remaining cheese and drizzle with butter.
Cover with aluminum foil (making a sort of tent so it doesn't stick to the cheese) and bake in preheated oven for 30 minutes.
Remove foil and bake 10 more minutes.
Serve and enjoy!