1. In medium skillet crumble and brown sausage with onions over medium heat.
2. Drain drippings, remove sausage mixture from skillet and drain on paper towels.
3. Transfer to mixing bowl.
4. Add sauerkraut, mayo, ketchup, mustard and cheese. Mix together well.
5. Spread approximately 1/3 cup filling on each bread slice until mixture is finished; cover with second slice to make sandwiches.
6. Lightly butter the outside of each sandwich and brown on griddle over medium heat until cheese is melted and bread is toasted.
7. Top with Thousand Island dressing if you like, or serve as is!