• 2 small boneless, skinless chicken breasts
  
• 2 teaspoons Italian seasoning
  
• Salt and pepper
  
• 2 tablespoons olive oil
  
• 4 tablespoons butter
  
• 1 small yellow onion, diced
  
• 3 cloves garlic, minced
  
• 4 tablespoons flour
  
• 1 ½ cups chicken broth
  
• ¾ cup milk
  
• 4 oz. cream cheese, softened
  
• 1 cup shredded cheddar cheese
  
• 10 oz. diced tomatoes & green chilies
  
• ½ lb. thin spaghetti
  
• 1 cup shredded mozzarella cheese
  
• Red pepper flakes and chopped parsley, for garnish

1. Prepare the Chicken (Optional)

1. Preheat the oven to 400°F.
   
2. Slice each chicken breast horizontally so you end up with two thinner pieces. Pat them dry, then season both sides with salt, pepper, and Italian seasoning.
   
3. Warm the olive oil in a large pot over medium-high heat. Cook the chicken for about 5–6 minutes per side, until golden and cooked through.
   
4. Remove the chicken and let it cool slightly before cutting it into bite-sized cubes.

2. Make the Sauce

1. Lower the heat to medium-low. Melt the butter in the same pot, scraping up any browned bits left behind; these will add great flavor.
   
2. Add the diced onion and cook for around 4 minutes, until softened. Stir in the garlic and cook for another minute.
   
3. Sprinkle the flour over the onions and mix until everything is coated. Let the mixture cook for about 2 minutes.
   
4. Gradually add the chicken broth, stirring between each addition so the mixture stays smooth.
   
5. Slowly pour in the milk, whisking until the sauce is fully combined.
   
6. Start heating a pot of water for the pasta. Cook the spaghetti according to the package directions and drain when ready.
   
7. Let the sauce gently simmer as the pasta water heats. Add the softened cream cheese and stir until it has completely melted into the sauce.
   
8. Reduce the heat to low and allow the sauce to cool slightly before adding the shredded cheddar. Stir until incorporated.
   
9. If you want the sauce a little looser, mix in a splash of the liquid from the canned tomatoes. Otherwise, drain the tomatoes and add them directly to the pot along with the chicken.
   
10. Stir in the cooked spaghetti. If your pot isn’t oven-safe, transfer everything to a greased 9×13 casserole dish.

3. Bake

1. Scatter the mozzarella over the top.
   
2. Bake uncovered for 15 minutes.
   
3. For a lightly browned, bubbly top, switch the oven to broil at 475°F for 1–2 minutes, keeping a close eye on it.
   
4. Remove from the oven and finish with red pepper flakes and chopped parsley.

• You can replace the cooked chicken with 2 cups of already-prepared chicken, such as leftover or rotisserie. Cooking the chicken in the pot, however, adds extra depth to the sauce.
  
• Shredding cheese from a block gives the smoothest melt; pre-shredded cheese tends not to melt as well.
  
• Add the cheddar only after the heat has been reduced so the sauce doesn’t separate.
  
• Thin spaghetti is ideal, but standard spaghetti, angel hair, or other pasta shapes will also work.

• Refrigerate leftovers in an airtight container for up to 3 days, or freeze for as long as 3 months. The sauce may change texture slightly after being frozen and reheated.