Cooking this lasagna is a step-by-step love letter to your taste buds. Here’s how to bring it all together:

1. Preheat your oven to 375°F (190°C).
2. Cook the lasagna noodles according to package instructions, then drain and set aside.
3. In a large skillet, heat olive oil over medium heat. Sauté the onions and garlic until they are translucent, about 5 minutes.
4. Add the mushrooms to the skillet and cook until they’re golden brown, another 5 minutes. Stir in the spinach, oregano, thyme, salt, and pepper, cooking until the spinach wilts. Remove from heat.
5. In a separate saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1-2 minutes, then gradually whisk in the milk, bringing the mixture to a simmer. Continue whisking until the sauce thickens, about 5 minutes.
6. Remove the sauce from heat and stir in the ricotta and half of the mozzarella cheese until smooth.
7. Spread a thin layer of the sauce in a 9×13 inch baking dish. Layer three noodles on top, followed by half of the mushroom-spinach mixture and a third of the remaining sauce. Repeat layers, ending with noodles and remaining sauce. Top with the remaining mozzarella and Parmesan cheese.
8. Cover with foil and bake for 20 minutes. Remove the foil and bake for another 10 minutes, or until the cheese is bubbly and golden.
9. Let the lasagna rest for 10 minutes before serving. This waiting time is crucial—it allows the layers to set, making serving easier and the experience richer.