In a medium saucepan, melt butter. Add flour, milk, salt, pepper, and nutmeg. Whisk until white sauce thickens and remove from heat.

Add 2 tbsp butter and 2 tbsp olive oil in a large skillet. Slice Monterey® Portabella® Mushrooms and place into hot skillet. Brown both sides. Once both sides are browned, remove mushrooms from heat and place in medium-sized bowl. *NOTE: If the mushrooms begin drying out, add a little more olive oil to the pan.

Return skillet to heat, add a tbsp of olive oil and spinach. Stir occasionally with tongs until spinach is wilted. Remove from heat.

In a glass 9x13" casserole dish, spread a layer of the white sauce. Add a layer of lasagna noodles. Add another layer of white sauce. Add a layer of mushrooms, spinach, and parmesan cheese. Repeat layers, ending with a layer of cream sauce and cheese.

Bake lasgna at 375 degrees for 40-45 minutes, or until lightly browned on top. Serve hot.