polenta gratin with spinach and mushrooms

From "Once a Month Mom"
NOTE: THIS RECIPE SERVES 4 for 3 dinners... That's 12 servings.
 
Ingredients
2    tablespoons olive oil           
10    cups mushrooms, sliced           
0.5 cups onion, chopped           
8 cups Spinach (more?)      
1 teaspoon Thyme           
1 teaspoon Nutmeg           
0.25    teaspoon Salt           
0.25    teaspoon Pepper           
1 tablespoons Butter, unsalted           
2 tablespoons Flour, all purpose, unenriched, unbleached           
0.75  cups Chicken broth (Can use broth from Crockpot cooked chicken night before)           
0.5 cups    Cream           
1  each dish Prepared Polenta           
2  cups Gruyere cheese, shredded           
                   
Directions:                   
1) In a large nonstick skillet, heat the olive oil. Add the mushrooms and cook over high heat, stirring occasionally, until lightly browned, about 6 minutes. Add the shallot/onion and cook over moderately low heat for 3 minutes. Add the spinach, thyme and nutmeg and cook over high heat until the spinach has wilted, about 2 minutes. Season with salt and pepper. Spread the spinach evenly in 8x8 foil pan.

2) In a small saucepan, melt the butter. Whisk in the flour over moderately high heat. Add the stock and cream and whisk until thickened, about 5 minutes. Season lightly with salt and pepper and pour over the spinach. Arrange the polenta slices on top of the spinach in overlapping concentric circles, pressing to submerge the polenta slightly. Sprinkle the Gruyère on the polenta, cover with foil and freeze until ready to serve.

To Serve: Preheat to 350, bake for 40 minutes. Once bubbling, Uncover and broil for  until golden. Let stand for 10 minutes before serving.                  
                   
Containers Needed:    2    Deep Dish 8x8 foil pan