3 tablespoons freshly grated Parmesan cheese
Preheat the oven to 400°F.
Heat 1 tablespoon of the oil in a large skillet until it is hot, but not smoking. Add the spinach, still wet from washing, and cook, covered, over medium-high heat for about 4 minutes, until wilted and soft. Add 1/4 teaspoon each of the salt and pepper and mix well. Spoon the spinach into a 6-cup gratin dish.
Bring 4 quarts of salted water to a boil in a large pot. Add the farfalle, stir, and cook for about 10 minutes, until tender but still slightly al dente. Drain the pasta in a colander, then cool it by running cold water over it for 30 seconds; drain well.
Toss the pasta with the fish, breaking up the fish if necessary, and spread it on top of the spinach in the gratin dish.
Heat the remaining tablespoon of oil and the butter in a large saucepan. Add the flour and mix well. Cook for 30 seconds, whisking, then add the milk and bring to a boil, stirring with the whisk. Add the remaining 1/2 teaspoon salt and 1/2 teaspoon pepper and mix well. Pour the sauce over the fish and pasta mixture and sprinkle the Parmesan cheese on top.
Bake the gratin for 25 to 30 minutes, until hot throughout and browned on top. Serve.
Reprinted with permission from Essential Pépin: More Than 700 All-Time Favorites from My Life in Food by Jacques Pépin, copyright (c) 2011. Published by Houghton Mifflin Harcourt.