Preheat your oven to 425 degrees F. This will ensure that your lasagna bakes evenly and the cheese melts perfectly.
Prepare water for the pasta in a large pot and bring it to a boil. Once boiling, add the whole wheat lasagna noodles and cook according to the package directions, shaving a few minutes off the time for a slightly firmer texture. This will help maintain the integrity of the pasta when layering in the lasagna.
While the pasta cooks, heat a large oven-safe skillet over medium heat and add the olive oil. Once the oil is shimmering, toss in the sweet onion and cremini mushrooms. Stir occasionally and cover the skillet; cook for about 10 minutes until softened. You want the onions to become translucent and the mushrooms to release their moisture, deepening in flavor.
Next, add the garlic cloves and fresh spinach to the skillet. Stir well and cook until the spinach wilts down, which should take just a few minutes.
Once the spinach is wilted, add the asparagus and toss everything together. Season the mixture with salt and pepper to taste. Let it all cook for another couple of minutes until the asparagus is tender-crisp.
In a small saucepan, melt the butter over medium heat. Once sizzling, whisk in the flour to create a roux. Cook this for about 1-2 minutes until it’s golden brown and has a nutty aroma.
Slowly add in the slow fat milk while whisking continuously to avoid lumps. Keep whisking until the mixture thickens, which will take about 5 minutes. You want it to be thick enough to coat the back of a spoon.
Stir in the parmesan cheese until melted, then season with a pinch of nutmeg, salt, and pepper. This cheese sauce will bring everything together!
Once the cheese is melted and the sauce is thickened, pour it over the sautéed vegetables in the skillet and turn off the heat. Gently fold in the cooked lasagna noodles, ensuring they’re well coated with the sauce.
Cover the top with scoops of the ricotta and sprinkle the freshly grated mozzarella cheese over it. This will create a lovely bubbly crust when baked.
Transfer the skillet to the preheated oven and bake for 15 to 20 minutes, or until the cheese is golden and bubbly. Keep an eye on it to prevent over-browning, and then remove from the oven.
Let it sit for a few minutes before serving. This allows the layers to settle. Serve with extra parmesan cheese on the side for those who want a little more flavor. Enjoy your homemade Springtime Veggie Skillet Lasagna!
