Preheat the oven to 350°F (175°C). Spray an 11×7-inch or 9×13-inch baking dish with nonstick cooking spray.
Cut four slices of rye bread into 2-inch cubes and place them in the bottom of the baking dish.
Pulse the remaining two slices of rye bread in a food processor to create fine breadcrumbs. Set aside.
Evenly distribute half of the pastrami over the cubed bread.
Spread the drained sauerkraut and chopped dill pickles on top. Sprinkle with 1 teaspoon of caraway seeds.
Add 2 cups of shredded Swiss cheese over the sauerkraut layer.
Place the remaining pastrami on top of the cheese. Gently press down on the layers to compact them.
Sprinkle the remaining 2 cups of shredded Swiss cheese and 1 teaspoon of caraway seeds over the pastrami.
In a medium bowl, whisk together the milk, beaten eggs, creamy dressing, and mustard.
Pour the sauce evenly over the entire casserole. Top with the prepared breadcrumbs. Cover with foil.
Place the dish in the oven and bake for 45 minutes.
Remove the casserole from the oven and let it rest for 5 minutes. Slice into portions and serve warm.
