
This creamy chicken tetrazzini is a comforting pasta bake loaded with tender chicken, mushrooms, and a rich cheesy sauce. It is hearty enough for a family dinner, easy to make ahead, and bakes up golden and bubbly straight from the oven.
Preheat the oven to 325°F (160°C). Lightly grease a 9 x 13-inch baking dish.
Heat 2 tbsp butter in a large pot over high heat. Add the chicken, season lightly with salt and black pepper, and cook for about 1 1/2 minutes until browned on the first side.
Turn the chicken, season again, and cook for 1 minute more until lightly golden. Transfer to a plate; it does not need to be fully cooked through at this stage.
Let the chicken rest for 5 minutes, then chop into small bite-sized pieces or shred with two forks.
In the same pot, melt the remaining 4 tbsp butter over high heat. Add the mushrooms and cook for about 4 minutes, stirring occasionally, until they soften and release their moisture.
Add the onion and garlic. Cook for 3 minutes, stirring often, until the onion softens and the mushrooms begin to turn golden. Season lightly with salt and black pepper.
Reduce the heat to medium. Sprinkle in the flour and stir for 30 seconds to coat the vegetables. Pour in the milk and stir well until the flour is fully dissolved and the sauce starts to thicken.
Add the cream, chicken stock, 1 tsp salt, and 1/2 tsp black pepper. Bring to a gentle simmer, stirring often, until the sauce thickens enough to lightly coat the back of a spoon. Do not reduce it too much, as it will continue to thicken in the oven.
Remove the pot from the heat. Stir in half of the cheese until combined, then add the cooked pasta and chopped chicken. Toss everything together until evenly coated. Taste and adjust the seasoning if needed.
Transfer the mixture to the prepared baking dish and spread it into an even layer. Sprinkle the remaining cheese over the top. Bake for 25 minutes, or until hot, bubbly, and lightly golden. Serve immediately.
If you do not have chicken thighs, boneless chicken breast works well but may be slightly less juicy. For the best texture, cook the pasta just to al dente so it does not soften too much while baking. Leftovers keep well in the refrigerator for up to 3 days and can be reheated with a splash of milk to loosen the sauce.