Step 1: Cook the Chicken

1. Prepare the Chicken: In a large Dutch oven or a heavy-bottomed pot, place the whole chicken. Sprinkle the chicken with 4 tablespoons of kosher salt. Add the bay leaf to the pot.
2. Add Water and Bring to a Boil: Pour enough water into the Dutch oven to fully cover the chicken. Ensure the chicken is submerged for even cooking. Place the Dutch oven over high heat and bring the water to a rolling boil.
3. Simmer the Chicken: Once boiling, reduce the heat to medium-low. Cover the Dutch oven tightly with a lid. Simmer gently for 1 hour, or until the chicken is cooked through and tender. The chicken is done when a meat thermometer inserted into the thickest part of the thigh reads 165°F (74°C). Simmering ensures the chicken cooks evenly and remains moist.
4. Remove Chicken and Reserve Broth: Carefully remove the cooked chicken from the Dutch oven using tongs or a slotted spoon. Place the chicken on a plate or cutting board to cool completely. It’s crucial to reserve the flavorful broth in the Dutch oven – this will be used to cook the spaghetti and adds depth of flavor to the casserole.
5. Cool the Chicken: Allow the chicken to cool completely, about 20 minutes. This makes it easier to handle and shred.
6. Discard Bay Leaf: Once the chicken is removed, locate and discard the bay leaf from the broth in the Dutch oven. The bay leaf has imparted its flavor and is no longer needed.
7. Skin, Bone, and Cut Chicken: Once the chicken is cool enough to handle, use your hands or a knife and fork to remove the skin and bones. Discard the skin and bones. Shred or cut the chicken meat into bite-sized pieces. Set the cooked chicken aside.

Step 2: Cook the Spaghetti

1. Preheat Oven: Preheat your oven to 350°F (175°C). This ensures the oven is ready when you assemble and bake the casserole later.
2. Reserve Chicken Broth: From the reserved chicken broth in the Dutch oven, remove and set aside ¼ cup of broth. This reserved broth will be used later to thin the cream of mushroom soup.
3. Bring Broth to a Boil: Return the Dutch oven with the remaining chicken broth to high heat. Bring the broth back to a rolling boil.
4. Cook Spaghetti: Break the uncooked spaghetti into thirds. This makes it easier to eat in the casserole. Add the broken spaghetti to the boiling chicken broth.
5. Cook Until Tender: Cook the spaghetti in the broth for 12 to 15 minutes, or until it is tender but still slightly firm to the bite (al dente). Cooking the spaghetti directly in the chicken broth infuses it with flavor.
6. Drain Spaghetti: Once the spaghetti is cooked, drain it well in a colander. Discard the remaining broth – the spaghetti has absorbed enough flavor.
7. Return Spaghetti to Dutch Oven: Return the drained spaghetti to the Dutch oven. Set aside.

Step 3: Prepare the Vegetable and Sauce Mixture

1. Melt Butter in Skillet: In a large skillet, melt 3 tablespoons of butter over medium-high heat. Allow the butter to melt completely and become slightly shimmering.
2. Sauté Vegetables: Add the chopped yellow onion, coarsely chopped green pepper, chopped celery ribs, and minced garlic to the melted butter in the skillet.
3. Sauté Until Tender: Sauté the vegetables for about 5 minutes, or until they are tender and fragrant. Stir frequently to prevent burning and ensure even cooking. Sautéing the vegetables softens them and develops their flavors, creating a delicious base for the casserole.
4. Add Sautéed Vegetables to Spaghetti: Pour the sautéed vegetable mixture from the skillet into the Dutch oven with the cooked spaghetti.

Step 4: Assemble the Casserole and Freeze (or Bake)

1. Prepare Soup Mixture: In a separate medium bowl, stir together the can of cream of mushroom soup and the ¼ cup of reserved chicken broth. Whisk until smooth and well combined. The reserved broth thins the soup to create a smoother sauce.
2. Add Soup Mixture to Spaghetti: Pour the cream of mushroom soup mixture into the Dutch oven with the spaghetti and vegetables. Stir well to combine and coat the spaghetti and vegetables evenly with the sauce.
3. Stir in Remaining Ingredients: Add the cooked chicken pieces, drained and chopped diced tomatoes, Worcestershire sauce, hot sauce, and freshly ground black pepper to the spaghetti mixture in the Dutch oven. Stir everything together thoroughly to ensure all ingredients are evenly distributed.
4. Season to Taste: Taste the mixture and add salt to taste, if needed. Remember that the chicken and broth were already salted, so taste before adding more.
5. Prepare Baking Dish: Lightly grease a 13- x 9-inch baking dish with vegetable cooking spray. This prevents the casserole from sticking and makes serving easier.
6. Spoon Mixture into Baking Dish: Spoon the chicken spaghetti mixture evenly into the prepared baking dish.
7. Top with Cheese: Sprinkle the shredded medium cheddar cheese evenly over the top of the casserole. Ensure the cheese covers the entire surface for a golden and cheesy crust.

To Freeze the Casserole (For Make-Ahead Meal):

1. Cool Completely: Allow the assembled casserole (before baking) to cool completely at room temperature. This is important before freezing to prevent condensation and ice crystals from forming.
2. Cover Tightly: Once cooled, cover the baking dish tightly with a double layer of plastic wrap, pressing it directly onto the surface of the casserole to minimize air exposure. Then, cover with a layer of heavy-duty aluminum foil. Ensure the casserole is completely sealed to prevent freezer burn and maintain quality.
3. Freeze: Place the covered casserole in the freezer. It can be frozen for up to 2 months. For best results, use within 1-2 months to maintain optimal flavor and texture.

To Bake the Casserole (If Not Freezing Immediately):

1. Bake: Bake the assembled casserole in the preheated oven at 350°F (175°C) for 15 to 20 minutes, or until the cheese is melted, bubbly, and lightly golden brown. The casserole is already cooked; baking is just to heat it through and melt the cheese.
2. Serve Hot: Once baked, remove the casserole from the oven and let it rest for a few minutes before serving. Serve hot and enjoy!

To Bake the Frozen Casserole:

1. Thaw Overnight: Remove the frozen casserole from the freezer and let it thaw overnight in the refrigerator. Thawing in the fridge is the safest method and ensures even heating during baking.
2. Preheat Oven: Preheat your oven to 350°F (175°C).
3. Bake: Remove the plastic wrap and foil from the thawed casserole. Bake in the preheated oven for 30 to 45 minutes, or until heated through and the cheese is melted and bubbly. Baking time may vary depending on your oven and how thoroughly thawed the casserole is. If the top starts to brown too quickly, you can loosely tent it with foil.
4. Serve Hot: Once heated through and bubbly, remove the casserole from the oven and let it rest for a few minutes before serving. Serve hot and enjoy your delicious make-ahead chicken spaghetti casserole!