Step 1

Melt butter in a saucepan over medium heat. Whisk in flour and cook 1 minute.

Step 2

Whisk in milk and nutmeg, bring sauce to a simmer, then reduce heat to low and cook until thick, whisking occasionally, 10 minutes.

Step 3

Season besciamella with salt.

Step 4

Preheat oven to 450℉.

Step 5

Toss tomatoes, onion, and garlic with oil; season with kosher salt and red pepper flakes.

Step 6

Transfer mixture to a baking dish; roast until tomatoes blister, 35-40 minutes.

Step 7

Purée mixtue in a food processor or with a handheld blender.

Step 8

Fill a large square deep casserole with the hottest tap water. Put the dry lasagna noodles in, and let the noodles soak for 20 minutes before draining.

Step 9

To prevent sticking, place the noodles in the water one at a time and swirl occasionally.

Step 10

When the noodles are done, stack in a single layer between sheets of foil coated with non stick spray. Finish

Step 11

Combine ricotta, 1 cup Pecorino, mozzarella, spinach, parsley, oil, garlic, and nutmeg for the filling; season with salt, black pepper, and red pepper flakes.

Step 12

To assemble cannelloni, spray the bottom and sides of a 3-quart baking dish with vegetable spray, then coat the bottom of the dish with Besciamella.

Step 13

Fill each lasagna sheet with a scant 1/4 cup filling and gently roll.

Step 14

Arrange cannelloni, seam sides down, in dish; spread 3 cups tomato sauce over the top, then sprinkle with remaining 1 cup Pecorino.

Step 15

Bake cannelloni 30 minutes; serve with remaining sauce on the side.