Preheat the oven to 350F degrees.

Start by sautéing the mushrooms in a pan with a drizzle of olive oil over high heat. Cook the mushrooms until the water evaporates. Add the butter, garlic, and season with salt and black pepper. Cook for another couple of minutes. Remove mushrooms from the pan and set aside.

Drizzle olive oil into the skillet if needed and add the ground Italian sausage. Cook for about 10 minutes until brown and crumbly. Season again and add fresh thyme.

Return the mushrooms back to the pan, combine, and set the filling aside.

To assemble the lasagna, start by adding a layer of béchamel sauce into a greased 8x8 inch baking dish. Spread one layer of the lasagna sheets on top. Continue with a layer of meat and mushroom mixture. Sprinkle cheese over the meat. Repeat the process for two more layers ending with a layer of béchamel sauce and cheese.

Bake in the oven for 30 minutes until bubbly and golden brown.

Heat a saucepan over medium-low heat. Add the butter and allow it to melt.

Add the flour. Continue to stir until the flour has absorbed all of the butter.

Continue to cook for 2-3 minutes, until the mixture smells slightly nutty but the color is still blonde.

Slowly drizzle in warm milk, continuously whisking until all of the milk is absorbed before adding any more. Continue to whisk until all the milk has been incorporated and the sauce is thick as a gravy consistency.

Add the salt, pepper, cayenne and nutmeg. Stir to combine.