Special equipment: waffle iron
Preheat the oven to 250 degrees F and prepare a cookie sheet with a cooling rack on top.
In a large bowl, add the rye flour, all-purpose flour, baking soda, baking powder and salt and whisk together to combine. Add the beer, milk, eggs and caraway seeds and whisk again until the wet and dry ingredients are mixed well, about 30 seconds.
Spray the waffle iron with nonstick spray. Pour about 1 cup batter into the preheated waffle iron and cook the waffle according to the waffle maker's instructions. As each waffle is cooked, place it onto the prepared rack in the oven to keep warm. There should be 8 waffles total, or 4 large waffles which can be cut in half.
Increase the oven temperature to 400 degrees F. Once all of the waffles are done, place 4 of them on a cutting board. Top each with a couple slices of cheese, some corned beef, about 1/2 cup of sauerkraut and drizzle with the Thousand Island dressing. Make a few layers, if desired. Top the sandwiches with the remaining waffles and place back on the rack. Place a sheet of foil on top of the sandwiches, add another cookie sheet on top of the foil and place a heavy pan or a brick on the sheet to press the sandwiches. Cook in the oven until the cheese melts, an additional 5 minutes.
Whisk all the ingredients in a small bowl until well incorporated. Store covered in the refrigerator.