Notes from the Test Kitchen:
This recipe is bursting with creamy goodness and flavor. The filling alone is fabulous... the chicken, cheeses, fresh spinach with all the seasoning and veggies is fabulous. Everything bakes up to perfection. Your whole family will love these!
chicken breasts, boneless and skinless, cubed into very small pieces
In a large pot, fill with water and cook manicotti tubes per package directions. Drain, rinse and set aside.
Swirl olive oil a few turns in a skillet over medium heat. Add chicken. Sprinkle with garlic salt and Italian seasoning. Cook, stirring often, until done - 7-8 minutes. Transfer to a bowl and set aside.
Add 2 tablespoons butter and another swirl of olive oil to the skillet over medium heat. Add mushrooms and cook 5-6 minutes. Add garlic and onion and continue to cook, stirring often, for another 5-6 minutes.
Add spinach and cook until wilted, 3-4 minutes. Season to taste with salt and pepper.
Remove from heat and add chicken, cream cheese and sour cream. Stir until incorporated and set aside.
In another skillet, add 3 tbsp butter and melt over medium-high heat. When melted, add flour and whisk constantly, 2-3 minutes, until lightly browned.
Whisk in milk and continue cooking, whisking constantly, until thick, about 3-4 minutes. Whisk in half of mozzarella, half of Monterey jack and 2 tbsp Parmesan, and whisk until incorporated and thick. The sauce should thickly coat the back of a spoon. Remove from heat.
Place some of the sauce on the bottom of the baking dish. Using a spoon, fill the manicotti tubes with the spinach/chicken mixture and place in the baking dish. Continue until all tubes are filled.
Pour the remaining sauce over the top of the pasta. Cover with foil and bake for 30-45 minutes. Remove foil, top with remaining cheeses and return to oven for 15 minutes.