Make the Russian Dressing:

1. Combine all dressing ingredients in a bowl and mix well.
2. Refrigerate for at least 20 minutes to let the flavors meld.

Prepare the Quick Sauerkraut:

1. In a bowl, dissolve sugar and salt in cider vinegar.
2. Heat grapeseed oil in a large pot over medium heat. Add the sliced onion and sauté for 2 minutes until softened.
3. Add the cabbage, vinegar mixture, water, and caraway seeds. Toss to combine.
4. Cover and cook on low heat for 15 minutes, stirring once after 10 minutes.
5. Transfer the sauerkraut to a container (including liquid) and let cool. Store in the fridge for up to 2 weeks.

Prepare the Pastrami:

1. Thinly slice the cold pastrami for easy handling.
2. Warm the slices with a few tablespoons of reserved cooking liquid (if available) in the microwave or oven.

Assemble the Reuben Sandwich:

1. Preheat the grill/broiler to medium-high. Place the rack about 10 inches from the heat source.
2. Toast the rye bread slices until lightly browned.
3. Spread butter on one side of each toasted slice. On the unbuttered side, spread 1 tablespoon of Russian dressing.
4. Layer the warmed pastrami on one slice of bread. Top with sauerkraut and a slice of Swiss cheese.
5. Place a slice of Swiss cheese on the other slice of bread.
6. Place both halves under the grill until the cheese melts.
7. Sandwich the halves together, slice diagonally, and serve immediately.