Step 1

Prepare the turkey: Stir together butter, thyme, garlic, rosemary, sage, lemon zest, 2 teaspoons of the salt, and 1 teaspoon of the pepper in a medium bowl until well incorporated. Rub butter mixture under turkey skin. Sprinkle outside of turkey with remaining 1 teaspoon salt and 1/2 teaspoon pepper. Pour chicken broth in bottom of a 6-quart slow cooker; add turkey, skin side up. Cover and cook on LOW until a thermometer inserted into thickest portion registers 165°F, 4 1/2 to 5 hours.

Step 2

Remove turkey from the slow cooker; remove skin from turkey and discard. Chop turkey and set aside, covered.

Step 3

Prepare the casserole: Preheat oven to 375˚F. Cook the bacon in a large skillet over medium until crisp, about 12 minutes; remove bacon. Reserve bacon drippings. Toss together the cubed white bread slices, melted butter, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper on a baking sheet. Bake in preheated oven until toasted, about 16 minutes.

Step 4

Whisk together the eggs, 2 cups milk, 1 1/2 teaspoons kosher salt, 1/2 teaspoon black pepper, and dry mustard in a large bowl. Stir in 2 oz. Parmesan, 10 oz. chopped cooked turkey (reserve remaining turkey for another use), cooked chopped bacon, 3 tablespoons bacon drippings, and bread cubes. Pour mixture into a lightly greased 11- x 7-inch baking dish. Bake in preheated oven until golden brown and set, about 45 minutes, shielding with foil during last 10 minutes to prevent excess browning, if needed.

Step 5

Whisk together unsalted butter and flour in a small saucepan over medium until smooth, about 1 minute. Gradually whisk in remaining 1 cup whole milk; cook until thickened and mixture just begins to bubble, about 4 minutes. Remove from heat; whisk in remaining 4 oz. Parmesan, 1/2 teaspoon black pepper, and 1/4 teaspoon kosher salt. Spoon sauce over casserole. Top with diced tomatoes, chopped parsley, and remaining 1/4 cup bacon.