Preheat oven to 350°F and grease baking dish.
Cut 4 slices rye into cubes, spread in dish.
Pulse remaining bread into crumbs; set aside.
Layer half of pastrami over bread.
Top with sauerkraut, pickles, and caraway seeds.
Sprinkle 2 cups cheese; top with remaining pastrami.
Whisk milk, eggs, dressing, mustard.
Pour mixture evenly over casserole.
Add breadcrumbs, remaining cheese, and seeds; bake 45 min.
Let rest 5 min before slicing and serving.
