Want Extra Mushroom Flavor?
Add a few extra mushrooms and sauté them until nicely browned before making the sauce. Don’t rush this step—the browning gives them so much flavor!!
How to Make Old Fashioned Chicken Tetrazzini
Step 1: Cook the Spaghetti
Preheat your oven to 375°F.
Bring a large pot of salted water to a boil and cook the spaghetti until just shy of al dente.
You don’t want it completely soft because it will continue cooking in the oven.
Drain well and set aside.
Step 2: Sauté the Mushrooms
Melt the butter in a large skillet over medium heat.
Add the sliced mushrooms and cook for about 5–7 minutes, stirring occasionally, until they soften and begin to brown.
Add the minced garlic and cook for another 30 seconds.
The smell at this point is incredible!!
Step 3: Make the Creamy Sauce
Sprinkle the flour over the mushrooms and stir well.
Cook for about 1 minute to get rid of the raw flour taste.
Slowly pour in the chicken broth while whisking constantly.
Once the mixture begins to thicken, stir in the heavy cream and sour cream.
Add the salt, black pepper, and dried thyme.
Let the sauce gently simmer for a few minutes until creamy and smooth.
Step 4: Add the Cheese
Remove the skillet from the heat.
Stir in the Parmesan cheese until melted into the sauce.
Taste and adjust the seasoning if needed.
Step 5: Combine Everything
In a large mixing bowl, combine the cooked spaghetti, chicken, creamy mushroom sauce, and frozen peas if you’re using them.
Give everything a good toss so the sauce coats all those noodles.
This is where it starts looking like the casserole you remember from family dinners.
Step 6: Transfer to the Baking Dish
Grease a 9×13-inch baking dish and spoon the spaghetti mixture inside.
Spread it into an even layer.
Sprinkle the mozzarella and cheddar cheese evenly over the top.
Don’t be shy with the cheese!!
Step 7: Bake
Bake uncovered for approximately 25–30 minutes, or until the casserole is hot and bubbling and the cheese is melted and lightly golden.
If you want a deeper golden-brown top, place it under the broiler for 1–2 minutes at the end.
Watch it closely—the cheese can go from gorgeous to too-dark surprisingly fast!!
Step 8: Let It Rest
Let the casserole sit for about 5–10 minutes before serving.
This gives the creamy sauce a chance to settle and makes the casserole much easier to scoop.
What to Serve With Chicken Tetrazzini
Because this casserole is rich and hearty, I like pairing it with something fresh and simple.
Try serving it with:
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