Creamed Spinach and Mushroom Casserole

Name: Creamed Spinach and Mushroom Casserole
Ingredients: Nonstick cooking spray, for the baking dish; 8 ounces (227 grams) cremini mushrooms, sliced; Kosher salt and freshly ground black pepper; 2 tablespoons unsalted butter; 1 shallot, thinly sliced; 2 cloves garlic, minced; 1 tablespoon all-purpose flour; 1/2 cup (125 milliliters) low-sodium vegetable broth; 1 cup (250 milliliters) milk; 1 teaspoon Dijon mustard; 1/2 cup (40 grams) finely grated Parmigiano-Reggiano cheese; Pinch freshly grated nutmeg; 8 ounces (227 grams) cooking spinach; 2 tablespoons finely chopped fresh parsley; 12 to 14 ounces (350 to 400 grams) frozen hashbrown patties or potato tots