In a large mixing bowl, beat cream cheese until fluffy.
Beat in sour cream, parsley salt and pepper.
Stir in chicken,
In a small skillet, cook onions and mushrooms in butter until tender; add to chicken mixture.
Stuff into manicotti shells.
In a large saucepan melt the butter.
Stir in flour and salt until smooth.
Gradually whisk in milk.
Bring to a boil; cook and stir for 2 minutes or until thickened.
Stir in 2 1/2 cups cheese and 2 tbs. parmasan cheese and boursin cheese just until melted.
Spread about 1/2 cup cheese sauce in each of the two greased 11x7x2 dishes.
Top with stuffed shells and remaining sauce.
Cover and bake 350 deg. for 25 min.
Uncover; sprinkle with remaining cheeses.
Bake 10-15 min longer or until bubbly and cheese is melted.
Can this be assembled entirely on Sunday and baked on Tuesday without the pasta turning to mush? Pasta tubes demand careful handling when shifted from refrigerator to hot oven because excessive moisture absorption causes structural collapse. Recognizing how starch behaves under prolonged refrigeration prevents this common kitchen failure. Three distinct structural stages govern this dish.
Thermal Management
Raw or par-boiled manicotti shells absorb liquid from surrounding sauces during storage, which dictates whether the final texture remains firm or becomes waterlogged. Chilling the assembled baking dishes uncovered for thirty minutes before wrapping them in heavy-duty aluminum foil helps set the dairy-heavy sauce and prevents condensation droplets from dripping onto the pasta. When baking straight from a 36°F refrigerator, increase the initial covered bake time from 25 minutes to 45 minutes at 350°F to ensure heat penetrates the dense core of cream cheese, sour cream, and shredded cheddar.
Freezing Mechanics
Stuffed tubes tolerate freezer storage up to two months if wrapped tightly in both plastic wrap and foil to prevent freezer burn, though dairy sauces may separate slightly upon thawing. Thaw the frozen pan in the refrigerator for 24 hours rather than using a microwave defrost cycle, which unevenly heats the delicate tubes and liquifies the Boursin-based sauce. Unbaking frozen pasta yields superior results compared to freezing a fully cooked dish because the starches do not undergo a second round of heat degradation.
Structural Substitutions
Italian-American baked manicotti evolved from traditional regional stuffed pasta traditions that originally utilized leftover roasted meats bound with soft cheeses. Swapping the cylindrical tubes for flat lasagna sheets requires layering the components in a 9x13-inch pan rather than individual 11x7-inch dishes, altering the baking footprint. Whisking the roux continuously while adding milk over medium heat prevents scorching at the bottom of the saucepan, guaranteeing a smooth béchamel base before the aged cheeses melt into the mixture.