10 ounces frozen chopped spinach, thawed and squeezed dry
1/2 cup plus 1 tablespoon freshly grated Parmesan cheese, divided
1/2 cup part-skim ricotta cheese
2 ounces lean ham, finely chopped
1/4 teaspoon freshly grated nutmeg
Preheat oven to 400°F.
Soak pasta in hot water for 10 minutes, stirring occasionally to prevent sticking.
Meanwhile, heat oil in a large nonstick skillet over medium heat. Add onion and cook, stirring occasionally, until beginning to color, 3 to 5 minutes. Add garlic and cook for 1 minute. Add tomatoes and basil; simmer, mashing the tomatoes with the back of a wooden spoon, until thickened, about 8 minutes. Season with salt and pepper and set aside.
Stir together spinach, 1/2 cup Parmesan, ricotta, ham and nutmeg in a medium bowl. Season with salt and pepper. Drain the noodles and blot dry. Spread each noodle with about about 2 generous tablespoons of the spinach mixture. Beginning with the short side, roll up each noodle around the filling. Cut each roll crosswise into thirds (or sixths if using 7-by-7-inch noodles). Stand each piece on end and score an X about halfway through the roll.
Spread 1/2 cup of the tomato sauce in the bottom of a shallow baking dish. Arrange the pasta rolls, scored ends up, on the sauce. Dab the remaining sauce over the pasta rolls, pressing lightly so that they open to form a ruffled top. Bake until heated through, 15 to 20 minutes. Sprinkle with the remaining 1 tablespoon Parmesan and serve.