Step 1

Wrap the spinach in a kitchen towel and squeeze to wring out as much moisture as possible. Put half of the spinach in a food processor; set the rest aside. Drain the ricotta in a large mesh strainer, stirring with a silicone spatula to remove as much liquid as possible.

Step 2

To the processor, add the ricotta, fontina, half of the basil, the egg, nutmeg, 1 teaspoon salt and ½ teaspoon black pepper. Process until smooth, about 1 minute. Add the Parmesan and remaining spinach, then pulse until finely chopped, 8 to 10 pulses. Transfer to a medium bowl, cover and refrigerate. Clean the processor bowl and blade, then return them to the base.

Step 3

Line a rimmed baking sheet with plastic wrap. In a large pot, boil 4 quarts water. Stir in 1 tablespoon salt, then add the lasagna noodles and immediately reduce to low. Cook, stirring occasionally, until just shy of al dente, 2½ to 3 minutes; do not simmer or boil. Reserve 1 cup of cooking water, then drain and rinse under cold water.

Step 4

Place 1 lasagna noodle on the counter with a short end facing you. Layer a second noodle so its bottom short end overlaps the first noodle’s top end by ½ inch (creating a single long sheet). Lightly press the overlap to seal. Place 1 cup filling in the center and spread it evenly, leaving a ½-inch border around all edges. Starting with the edge closest to you, roll into a tight cylinder, using a finger to wipe clean any excess filling at the far end as you finish rolling. Press the overlap to seal.

Step 5

Holding the roll in one hand, use a butter knife to smooth any filling that is spilling out. Place the roll seam down on the prepared baking sheet. Repeat 4 times, making 5 rolls total. Cover with plastic wrap, then freeze until firm enough to hold their shape when cut, about 1½ hours.

Step 6

To make the sauce, in the processor, puree the tomatoes with juices until mostly smooth, about 20 seconds. In a medium saucepan over medium, combine the oil and garlic. Cook, stirring, until starting to brown, 1 to 2 minutes. Discard the garlic, then add the tomatoes, pepper flakes, remaining basil, 1 teaspoon salt, ½ teaspoon black pepper and reserved pasta water. Simmer, uncovered and stirring, until slightly thickened, 6 to 8 minutes. Off heat, taste and season with salt and pepper.

Step 7

About 20 minutes before ready to bake, heat the oven to 400°F with a rack in the middle position. Set aside 1½ cups sauce for serving; spread the remainder in a 9-by-13-inch baking dish. Using a chef’s knife, cut each chilled pasta roll crosswise into 4 slices, each about 1 inch thick. Arrange the slices cut side up in a single layer over the sauce. Tightly cover the baking dish with foil and bake until the sauce is bubbling, 35 to 40 minutes

Step 8

Remove from the oven, uncover and let stand 10 minutes. In a small saucepan over medium, heat the reserved sauce. Spoon ¼ cup sauce onto serving plates, then use a spatula to set a few rolls on top of the sauce on each plate. Sprinkle with additional Parmesan.