Lasagna and baked pastas are an ideal canvas for leftovers like chicken and ham. Here, we bring the two together for a spin on chicken cordon bleu, complete with spinach, creamy swiss cheese, and a dash of nutmeg.
Melt butter in a large saucepan over medium-low heat. Whisk in flour and cook, stirring, as mixture bubbles, 2-3 minutes. Add milk a little bit at a time, whisking smooth after each addition, until all of the milk has been added. Bring to a boil and reduce to a gentle simmer, whisking to prevent scorching.
Season with 1 teaspoon salt and ½ teaspoon black pepper and cook, whisking often, until sauce is thick and has lost the raw flour taste, about 10 minutes.
Remove from heat; stir in nutmeg. Taste and add more salt if needed. Use warm, or transfer to a bowl and cover the surface with plastic wrap to prevent a skin from forming.
Melt butter in a large skillet over medium high heat. Add garlic and cook until fragrant, about 30 seconds. Add half of spinach, cover, and cook for a minute to wilt. Toss, season with salt and pepper, and add remaining spinach. Cover and cook for another minute. Toss and cook until spinach is fully wilted, about 2 minutes. Transfer to a colander and use the back of a spoon to press out extra liquid.
Preheat oven to 375°F. Grease a 9×13 baking dish and set aside.
Bring a large pot of water to a boil. Add salt and lasagna noodles. Cook to al dente according to package instructions. Drain, arrange on a baking sheet and toss with olive oil to prevent sticking.
Spread ½ cup bechamel on the bottom of the prepared dish. Arrange 4 noodles in the dish and top with a third of the ham, a third of the chicken, a third of the spinach, a third of the of gruyere and 1 cup of bechamel. Repeat layering 2 more times, using half of the fillings for the second layer and the remaining amount of filling for the final layer.
Top with remaining 4 lasagna noodles, the remaining bechamel and sprinkle evenly with parmesan.
Cover with foil and bake for 30 minutes. Remove foil and bake 30 more minutes, until bubbly and golden brown on top. Let stand 10 minutes before serving.