Heat oven to 350 degrees. Mist an 8- by 8-inch pan, 9- by 9-inch pan or 6- to 8-cup soufflé dish with non-stick spray and set aside.
In a large skillet, add spinach and water. Wilt spinach over high heat, tossing several times to cook evenly. Spinach should be wilted in only 3-5 minutes. Remove from heat and set aside.
In a large bowl, combine all ingredients (including spinach and its water), stirring until blended. Season with ground pepper and salt if desired. (If cheese is salty, do not salt at this point; wait until you taste the finished product.) Pour mixture into prepared dish.
Bake until mixture is set in center, about 75 minutes. Let stand 10 minutes before serving.
Cheese variations: Use Swiss cheese instead of sharp cheddar and add 1/4 teaspoon ground nutmeg instead of garlic. If you use feta instead of sharp cheddar, add 1/2 teaspoon dried oregano instead of garlic. If you use Gorgonzola instead of sharp cheddar, simply omit the garlic.