• In a large pan over medium to medium-high heat, cook the sausage, breaking it into crumbles with a wooden spoon. Cook for about 10 minutes, stirring occasionally, until browned and crispy. Transfer to a bowl and leave the rendered fat in the pan.
• In the same pan with the sausage fat, add the sliced leeks. Cook over medium heat for 8–10 minutes, stirring often, until softened and lightly caramelized.
• Pour in the white wine and use a wooden spoon to scrape up any browned bits. Simmer for 2–3 minutes until most of the liquid is absorbed. Transfer leeks to a bowl.

Béchamel Sauce

• In a medium saucepan over medium heat, melt the butter. Whisk in the flour and cook for 1 minute, whisking constantly, until the mixture smells slightly nutty and no longer like raw flour.
• Slowly whisk in about ½ cup of the milk until smooth. Gradually add the remaining milk, whisking constantly to avoid lumps. Bring to a gentle boil, then reduce heat to medium and continue whisking for about 10-15 minutes until the sauce thickens and coats the back of a wooden spoon.
• Once thickened, season with salt, black pepper, and nutmeg. Stir to combine, then remove from heat.

Green Sauce

• In the same large pan from the sausage and leeks, heat the olive oil over medium heat. Add the smashed garlic, peas, and a large handful of spinach. Stir as the spinach wilts, then continue adding more spinach by the handful until it all fits and is wilted, about 3–5 minutes total.
• Transfer the cooked greens to a blender. Add basil, crème fraîche, salt, and pepper. Blend on high until smooth.
• Add ½ cup water and blend again until the sauce is smooth and pourable. Taste and adjust seasoning as needed. Add more crème fraîche for creaminess or more water if the sauce is too thick.

Assemble and Bake Lasagna

• Preheat oven to 400°F (200°C).
• In a 9"x13" baking dish, spread a thin layer of béchamel. Top with 4 no-boil lasagna sheets. Spread ⅓ of the remaining béchamel over the noodles, followed by half of the green sauce. Evenly sprinkle half the sausage and leeks, then scatter 4 ounces of torn mozzarella and ⅓ of the Parmesan.
• Repeat with another layer of 4 lasagna sheets, ⅓ of the béchamel, remaining green sauce, sausage, leeks, another 4 ounces mozzarella, and ⅓ Parmesan.
• Top with the final 4 lasagna sheets, the remaining béchamel, 8 ounces mozzarella, and the rest of the Parmesan.
• Place the dish on a sheet pan to catch drips and bake uncovered for 40–45 minutes until golden, bubbling, and heated through. Optional: broil for 2–3 minutes at the end for a deeper golden top. Watch closely to prevent burning!
• Remove from the oven and let rest for at least 20 minutes before slicing into 12 portions. Garnish with fresh basil and extra grated Parmesan, if desired.