the remaining 2 tablespoons butter, and heat until melted.
Add the flour and cook, whisking constantly, until light
golden blond. Slowly pour in the milk, whisking
constantly. Bring to a simmer, then remove from the heat
and stir in two-thirds of the mozzarella and the Parmesan,
then season to taste with salt and pepper.
To assemble the lasagna, dry the baking dish and grease
with butter. Spread 1 cup of the cheese sauce in the
bottom of the dish. Lay 3 noodles on top of it, spacing
them evenly (the noodles will not quite touch each other;
this is fine). Top the noodles evenly with half of
mushroom mixture and then with another 3 noodles. Top
with half of spinach/cottage cheese mixture and another 3
noodles. Repeat the layers with the remaining mushroom
mixture, spinach mixture, and noodles, ending with a
layer of noodles. Pour the remaining cheese sauce over
the top and spread it evenly. Sprinkle the remaining
mozzarella evenly over the top.
- Place a foil-lined baking sheet on the lower oven rack to
catch any drips, then place the lasagna on the rack above
it. Bake until the lasagna is bubbling around the edges,
about 20 minutes. Turn on broiler on and broil until the
top is lightly browned, about 5 minutes (if you have an
under-oven broiler, transfer the lasagna to the broiler
after baking). Let cool for 10 minutes, then slice and
serve.