Topping:
4 slices white sandwich bread, torn into quarters (I used a long forgotten bread bowl tucked in the back of the freezer – thawed it in the microwave before using)
2 tablespoons butter, melted

Filling:
3 pounds russet potatoes (about 4-5 medium), peeled and sliced 1/8-inch thick
1 teaspoon salt
4 tablespoons butter
1 medium onion, chopped
1 teaspoon dried thyme
3 medium garlic cloves, finely minced
6 tablespoons all-purpose flour
2 cups low-sodium chicken broth
3/4 cup heavy cream or milk
6 ounces Swiss cheese, shredded, about 2 cups
2 tablespoons Dijon mustard
1/4 teaspoon cayenne pepper
2 pounds boneless, skinless chicken breasts, trimmed of excess fat and sliced thinly
9 ounces deli ham, chopped
2 tablespoons minced fresh parsley leaves