Step 1

For the pesto (if making), preheat the oven to 425°F

Step 2

Cut off the top of the head of garlic and place on a piece of foil

Step 3

Drizzle the 2 tablespoons olive oil over the exposed cloves and season with salt and pepper

Step 4

Wrap tightly and roast until brown and caramelized, 40 to 45 minutes

Step 5

Let cool

Step 6

When the garlic is ready, lightly pulse the pistachios in a food processor

Step 7

Squeeze in the roasted garlic cloves, add the basil and Parmigiano-Reggiano and season with salt and pepper, then process while slowly adding the ½ cup olive oil until smooth

Step 8

Transfer to a medium mixing bowl and reserve

Step 9

Makes 2 cups

Step 10

Preheat the oven to 375°F

Step 11

For the bechamel, melt the butter in a large saucepan over medium heat

Step 12

Add the flour and whisk until it begins to smell nutty and fragrant, about 1 minute

Step 13

Slowly stream in the milk while whisking so that no lumps form and the mixture remains smooth

Step 14

Season with nutmeg

Step 15

Once the bechamel sauce comes to a low bubble, continue to cook and let thicken for 5 to 6 minutes, whisking often

Step 16

Remove from heat, whisk in the Parmigiano-Reggiano and reserve

Step 17

For the ricotta mixture, add the ricotta and egg to the bowl of pesto and stir to combine

Step 18

Reserve

Step 19

To assemble the lasagna, evenly spread 1 cup of the bechamel sauce in the bottom of a 13-by-9-inch pan (I prefer a disposable aluminum pan for easy clean up!)

Step 20

Top with 4 lasagna noodles, 1/3 of the ricotta mixture, 1 cup of the mozzarella cheese, 1/3 of the spinach, 1/3 of the cooked sausage and 1 cup of the bechamel

Step 21

Repeat, starting with 4 lasagna noodles and ending with 1 cup of the bechamel

Step 22

To finish, top with 4 lasagna noodles, the remaining ricotta mixture, 1 cup of the mozzarella cheese, the remaining spinach, remaining sausage and remaining 4 lasagna noodles

Step 23

Top the noodles with the remaining bechamel and mozzarella cheese

Step 24

Tightly cover the lasagna in aluminum foil and place on a large baking sheet

Step 25

Bake until hot in the middle, 55 to 60 minutes

Step 26

Remove the foil and bake until bubbly and browned on top, 15 to 20 minutes more

Step 27

Allow lasagna to set for 15 minutes before cutting into it

Step 28

Garnish with parsley and serve