Early in the day, make the required amount of polenta and spread it in an 8" by 16" baking dish or sheet. (I used a 8" by 8" square dish for my half recipe.) Put this in fridge to set.
Make a bechamel (bescimella) sauce with butter, flour, milk, and cream. When this is thick, season with salt, pepper, and grated Parmesan. Meanwhile, sauté some sliced mushrooms. I used about half and half pleurote gris/oesterzwammen/oyster mushrooms and shiitakes.
Now cut the slab of polenta in half. The larger size would be cut in half, giving two 8" by 8" squares. I cut my 8" square on the diagonal. Put one of the pieces in a casserole dish; top with half the mushrooms, then half the bechamel. Put the remaining bit on polenta on that, add the remaining mushrooms and bechamel. Top with a bit more grated Parmesan, then bake for 375F for 25-30 minutes. Cut into pieces are serve at once. Yum, a very pleasing dish. Even though it was very good, we thought it might be quite nice with some lardons (or chopped bacon, perhaps) sautéed with the mushrooms.
December at Cookbook Countdown means folks can cook from books they've used during the year, or start with a new one. Why don't you choose a cookbook from your shelf and join in?