Preheat your oven to 425°F and place the oven rack in the center position. Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the sliced cremini mushrooms and sprinkle with 1 teaspoon salt. Let them cook undisturbed for about 5 minutes until they start to brown. Stir occasionally and continue to cook until golden and caramelized, about 5 minutes more. Transfer the cooked mushrooms to a plate and set aside.

Reduce the heat to medium and add the remaining 2 tablespoons olive oil to the skillet. Sauté the minced shallots, stirring frequently until softened. Add the minced or grated garlic and cook until fragrant, about 1 minute. Stir in the butter until melted. Sprinkle the flour over the mixture and cook, stirring often, for 2-3 minutes to form a blonde roux. Gradually pour in the whole milk, whisking constantly until smooth. Incorporate the Italian herb blend, garlic powder, black pepper, and freshly grated nutmeg. Cook and stir until the sauce thickens. Remove from heat and stir in the sour cream and grated Parmesan cheese until fully combined. I like to grate the nutmeg fresh for a deeper, warm flavor. Cover the sauce and set aside.

Bring a large pot of salted water to a boil over high heat. Add the lasagna noodles and cook until al dente, following the package instructions to avoid overcooking. Drain the noodles in a colander and arrange in a single layer on a plate to prevent sticking. This step will make assembling the lasagna much easier later. If you're using fresh noodles, blanch them briefly until just flexible.

Coat a 9x13-inch baking dish with non-stick oil spray. Arrange your work area with separate bowls for the prepared sauce (from Step 2), lasagna noodles (from Step 3), ricotta cheese, chopped basil, shredded Gruyere, and mushrooms (from Step 1).

Spread 4–5 tablespoons of béchamel sauce (from Step 2) on the bottom of the prepared baking dish. Add a layer of cooked lasagna noodles (from Step 3), about 4 noodles per layer. Then, top with 1/3 of the béchamel sauce, 1/3 of the ricotta, 1 tablespoon chopped basil, 1/3 of the Gruyere cheese, and 1/3 of the caramelized mushrooms (from Step 1). Repeat this layering process twice more for a total of 3 full layers, finishing with sauce and cheese on top. For even more depth, I sometimes sprinkle a little extra Parmesan on the very top layer if I have any left.

Lightly spray one side of a sheet of foil with oil spray and cover the lasagna dish (oiled side down). Place the baking dish on a rimmed sheet pan and bake in the preheated oven for 30 minutes. Remove the foil and continue baking for another 15 minutes, or until the lasagna is bubbly and slightly browned around the edges.

Let the baked lasagna rest outside the oven for 10 minutes to allow the layers to set—this makes serving much neater. Before serving, sprinkle with freshly chopped parsley for a burst of color and freshness. I love this finishing touch as it really livens up the dish.