Reuben Mac and Cheese

Ingredients

• 3 slices rye bread torn
• ⅓ cup panko bread crumbs
• 1 (16 ounce) package egg noodles
• 3 tablespoons butter
• 1 cup chopped onion
• 1 teaspoon salt
• ½ teaspoon ground black pepper
• ¼ cup spicy brown mustard
• 3 tablespoons all-purpose flour
• 3 cups hot milk
• 3 cups shredded Swiss cheese or more to taste - divided
• 1 ½ cups sauerkraut drained (reserve juice)
• ½ pound deli sliced corn beef or more to taste
• 3 tablespoons butter melted