Combine all ingredients in a small dish. Cover and refrigerate to allow flavours to meld. (Can be made upto a day ahead)
Assembly
Preheat panini maker or heavy skillet. Butter one (outer) side of each slice (optional). On the inner side, divide corned beef equally between 4 slices of bread. Then top beef with one quarter of sauerkraut and one quarter of cheese slices. Slather Russian Dressing on the other side. Top the cheese with last 4 slices of bread, Russian Dressing side down.
Toast in skillet or panini maker until cheese is soft and bread is toasted. Flip sandwich half way if using a skillet.
Serve warm with dill pickles on the side if desired.
Alternative: Toast unbuttered bread in a regular toaster, assemble beef, sauerkraut, cheese and Russian dressing as outlined above. Microwave 3- seconds to a minute to soften cheese and warm sandwich.Alternative: You can substitute Thousand Island Dressing for Russian Dressing.
Notes
Note 1: You can buy prepackaged corned beef slices at the deli or to make your own start with a pre-spiced corned beef (like Rachel's). Rinse off spices, trim as much visible fat as possible and cook in a slow cooker with 1 cup of beer 4 hours on high or 7 hours on low. Cool and slice.Note 2: You can use drained sauerkraut out of a can directly but you can also drain sauerkraut, add 1 teaspoon of caraway seeds, 1 cup of beer and cook in a slow cooker 2 hours on high or 3 hours on low.