04Add in onions, mushrooms and the garlic; stir until softened (about 4 minutes).
05Whisk in the flour, salt, pepper and nutmeg, whisk for 2 minutes.
06Gradually add in the cream, continue whisking until thick and until the mixture reaches a light boil, remove from heat then mix in 1/4 cup grated Gruyere or Swiss cheese, stir until cheese melts, (taste for extra seasoning).
07In the prepared casserole or baking dish spread half of the spinach, then top the spinach with 2 Tbsp grated Parmesan cheese; then cover with half of the mushroom/cream sauce, then repeat.
08Sprinkle with 1/2 cup grated Gruyere or Swiss cheese.
09Bake for 25-35 minutes, or until hot and bubbly.