Toss asparagus in olive oil and place on parchment-lined sheet pan. Sprinkle with a pinch of salt and pepper. Place in oven and cook until fork tender, about 7-10 minutes depending on the size of asparagus spears.
While asparagus is cooking, make the béchamel. Melt butter in large saucepan over medium heat. Add leeks and sauté a few minutes until tender. Add flour and stir a few minutes longer. Slowly whisk in milk and cream. Cook, whisking constantly, until mixture thickens and begins to bubble, about 5-7 minutes. Remove pan from heat and stir in salt, pepper and nutmeg.
Assemble lasagna*: Pour a small ladle of béchamel into the bottom of a rectangular baking dish, spreading it evenly. Place 2 sheets of lasagna on top of the sauce. Spread ¼ of the roasted asparagus, followed by shredded Toma, and finally a bit more béchamel on top. Continue with a few more layers, ending with lasagna noodles. On top of the final layer, spread béchamel and grated Toma. Nestle the remaining asparagus spears on top of the cheese.
Bake lasagna for 20-30 minutes until the top is browned and bubbly. Let lasagna rest for 10-15 minutes to set enough to be cut and served.
*We used a deep pan (7” x 10” x 3.5” deep). You’ll need to adjust assembly instructions and number of layers to fit a different size pan.
