If using dried lasagna noodles, cook according to package directions in very salty water until 5 minutes less than al dente. Drain and set aside.

Lay the noodles out on a lightly oiled baking sheet in a single layer.

Heat a large saucepan over medium-high heat and drizzle in the olive oil.

Add onion and garlic to pan and stir. Cook for 1-2 minutes until onion softens.

Add sliced mushrooms and cook for 4-5 minutes until onion is translucent.

Add salt and pepper to taste.

Add flour and stir to combine. Let cook for 30 seconds.

Add vegetable stock little by little, stirring to break up lumps. Bring to a simmer and cook for 8-10 minutes.

Add heavy cream and stir. Return to a simmer and cook for another 8-10 minutes until thickened.

Turn off the heat, add spinach and ⅔ of the parmesan cheese, stirring until spinach wilts.

Taste the sauce and adjust seasoning if needed.

Heat oven to 375°F.

Spread a thin layer of sauce in a medium-sized baking dish. Layer lasagna noodles, sauce, and mozzarella cheese. Repeat until ingredients are used up.

Top with remaining mozzarella and parmesan cheese.

Bake for 30-40 minutes until cheese has melted and edges are browned.

Let cool for 10 minutes before serving. Garnish with parsley.