1 pound asparagus, woody ends removed
1 teaspoon olive oil
1 pinch salt
3 tablespoons butter
3 tablespoons flour
3 cups whole milk
1/2 teaspoon salt
1/4 teaspoon pepper
1 pinch freshly grated nutmeg
2 cups (packed) baby spinach leaves
1 cup store-bought pesto
1 pound no-boil lasagna noodles
1 cup grated Parmesan cheese
Preheat the oven to 450 degrees fahrenheit.
Toss the whole asparagus spears with the olive oil and salt. Place in a single layer on a baking sheet and roast for 10 minutes, until caramelized. Remove the asparagus from the oven and set aside the four most aesthetic spears. Cut the rest into 1-inch lengths and set aside. Reduce the oven temperature to 350.
Meanwhile, heat the butter in a saucepan over medium-low heat. Add the flour and whisk together. When the mixture just begins to froth, drizzle in 1/4 cup of the milk and whisk well to combine. Keep adding milk by 1/4 cupfuls, whisking well after each addition, until all of the milk has been added. Keep cooking the béchamel until it just barely begins to bubble, then remove from the heat and season with salt, pepper, and nutmeg.
Place the spinach in a nonstick skillet with a tablespoon of water. Cook, stirring continuously, over medium heat, until the spinach is completely wilted. Chop and set aside.
Spread about 1/4 cup of the béchamel sauce over the bottom of a casserole dish. Add a layer of lasagna noodles, followed by 1/2 of the spinach. Spread 1/3 of the pesto over the top, and add 1/2 of the chopped asparagus. Top with 1/3 of the béchamel, and sprinkle with 1/3 of the cheese.
Top with more noodles and add the remaining spinach, another 1/3 of the pesto, the remaining asparagus, another 1/3 of the béchamel, and another 1/3 of the cheese.
Place a final layer of lasagna noodles over the top. Spread with the remaining pesto and the remaining béchamel, and arrange the reserved whole asparagus spears over the top. Cover the entire lasagna with foil.
Bake for 30 minutes, then remove the foil and sprinkle the remaining Parmesan over the top. Continue baking for an additional 10 minutes, or until bubbly and browned.
Allow to cool for 30 minutes before serving.