Preheat oven to 350°F. Spray a 2-quart (or an 11x17) baking dish with nonstick cooking spray; set aside.
In a 12-inch skillet, brown sausage (1 pound) and cook until there is no longer any pink. Drain grease.
In a mixing bowl, mix together soup (1 can), milk (3/4 cup), chopped onion (1/2 cup), salt (1/4 teaspoon), black pepper (1/4 teaspoon), dried thyme leaves (1/2 teaspoon), dried sage (1/4 teaspoon), and Worcestershire sauce (2 teaspoons) until evenly combined.
In the prepared baking dish, layer half the potatoes, soup mixture, and sausage. Repeat layers.
Cover baking dish tightly with aluminum foil. Bake in the preheated oven until potatoes are soft, about 60 minutes. Remove from oven, uncover, and sprinkle top with cheese (2 cups). Return, uncovered, to the oven, and bake until cheese is melted about 4-5 minutes. Garnish with parsley (2 tablespoons) and serve.
Sausage: I use regular ol' bulk pork sausage for this recipe. But that doesn't mean you can't experiment. Use your favorite crumbly sausages for a delicious twist all your own!
Cream of Mushroom Soup: I like to use the low sodium version of this soup.
Milk: You can use any type of milk you have on hand. I like whole milk best.
Onion: Yellow onion is my choice in this casserole.
Worcestershire sauce: Adds a lot of richness, depth of flavor, and umami taste.
Potatoes: I use russet potatoes in this casserole and hand-cut them about 1/4 inch thick.
Cheese: Most people would use something mild for a sausage potato bake cheese topping -- or even none at all, the horror! But I use sharp cheddar with this recipe to give you a nice pop of cheddar goodness to offset the heavy, savory sausage.