Heat a large pan over medium-high heat. Melt 6 tablespoon (¾ stick) butter and then add flour; whisk constantly for 30 seconds or until foaming. Whisk in the Milk, Salt and Pepper; bring to a boil, then reduce heat and simmer for 8 minutes - stir occasionally - until thickened.
Spread/lay ingredients into the 8 Inch Baking Sheet in the following order-Milk/Flour Mixture-Oven-Ready Lasagna Sheets-Very Thinly Sliced-Thinly Sliced Squash-Milk/Flour Mixture-Oven-Ready Lasagna Sheets-Very Thinly Sliced-Thinly Sliced Squash-Milk/Flour Mixture-Oven-Ready Lasagna SheetsTop with the Gruyère, cover with foil and put into the oven; bake for 60 minutes or until the noodles are tender.
Uncover and broil until the top is golden brown; a few minutes longer. Allow the lasagna to rest for about 10 minutes before serving.