Found this in Cookie Magazine. I made this on Feb. 7, 2009. It was fairly easy to put together and is a nice different twist on lasagna -- if you are a fan of sweet potatoes and spinach, that is!
1 small onion, chopped
2 celery stalks, chopped
1 carrot, chopped
1 teaspoon red-pepper flakes (or to taste)
2 tablespoons olive oil
1 tablespoon flour
1 cup milk, plus one tablespoon
1/4 teaspoon freshly grated nutmeg
3 to 4 large sweet potatoes, peeled and thinly sliced (ideally with a mandoline)
1 6-ounce package frozen spinach, thawed and drained (I used twice as much)
1/2-pound ball fresh mozzarella, sliced thinly (I used more, and don't expect it to fill up whole layers)
1 cup fresh ricotta (again, I used about twice as much)
3/4 cup Parmesan, grated
In a medium saucepan over medium heat, sauté the onion, celery, carrot, and red-pepper flakes in the olive oil until the vegetables are soft, about 10 minutes. Add the flour and stir for about a minute. Whisk in the milk and nutmeg and heat until warmed through. (Note: Will be pretty liquidy when you layer it.)
Spread one-third of the onion mixture on the bottom of a 9-by-13-inch baking dish. Layer one-third of the potatoes, mozzarella slices, ricotta, spinach, and Parmesan and repeat in three layers, ending with just Parmesan, mozzarella, and a little milk around the edges.
Bake, covered with foil, at 425 °F for 1 hour, removing the foil for final 10 minutes so the top can crisp up and get bubbly.
Notes: I had lots of sweet potato slices left over so I tossed them with melted butter (1 T), 2 T brown sugar and 1 t cinnamon and baked at 375 for about 25 minutes to get sweet-potato cinnamon chips. They didn't crisp up like potato chips though.