White Lasagna

Preparation

1. Step 1

   Heat oven to 400 degrees. Grease a 9-by-13-inch baking pan with a little butter.

2. Step 2

   Prepare the béchamel: In a large saucepan, melt 4 tablespoons butter over medium heat. Once melted, add flour and whisk until combined. Cook for 4 to 5 minutes, or until pale golden. Slowly whisk in the milk, a little at a time, so that the sauce does not clump. Add the salt, nutmeg and bay leaf. Gently bring to a simmer and let cook for 9 to 12 minutes, whisking often, until the béchamel is thick but still pourable. Stir in ½ cup Parmesan and grated garlic, and taste, adding more salt if needed.

3. Step 3

   While the béchamel is cooking, start preparing the filling: Place a 12-inch skillet over medium-high heat and add 1 tablespoon olive oil. Let it heat until it thins out, about 30 seconds, then add the asparagus and sauté, shaking the pan, until crisp-tender, 4 minutes. Season with salt and pepper, then transfer to a medium bowl and stir in the frozen peas and 2 tablespoons herbs.

4. Step 4

   Add remaining 2 tablespoons oil to the pan and heat until the oil thins out, about 30 seconds, then add the leeks, fennel seeds, red-pepper flakes and ¾ teaspoon salt. Sauté leeks until tender and golden at the edges, 4 to 6 minutes. Add the spinach and remaining herbs, working in batches if needed, and sauté until the greens are very tender and the pan is very dry, about 10 minutes. Stir in lemon zest and juice. Taste and add more salt if needed. It should be well seasoned.

5. Step 5

   Add mixture to a large bowl. Stir in ricotta and ¾ cup each Parmesan and pecorino (save remaining Parmesan for the top). Taste and add more salt if needed.

6. Step 6

   Remove bay leaf from béchamel, then ladle some of the sauce into the bottom of the baking pan until just covered. Place as many noodles as will fit on top of the béchamel, breaking or cutting them to fit in one layer. Ladle a little more béchamel on top of the noodles, covering the surface. Add half of the ricotta mixture, spreading evenly, then sprinkle half of the asparagus-pea mixture on top. Add another layer of noodles, then béchamel, then the remaining ricotta mixture, then the remaining asparagus-pea mixture. Top with the sliced mozzarella. Add a third and final layer of noodles (don’t worry if you don’t end up using all of the noodles) and cover with remaining béchamel. Sprinkle with remaining ½ cup Parmesan.

7. Step 7

   Cover the pan with foil and place on a rimmed baking sheet to catch any drips. Bake for 30 minutes, then remove foil. Bake for another 30 to 40 minutes, or until golden brown and bubbling on top. (If the top is still pale, you can run the lasagna under the broiler for 1 to 3 minutes.) Let sit for 20 to 30 minutes before serving.