Preheat your oven to 400°F and thoroughly coat a 9×13-inch baking dish with non-stick cooking spray. Pat the thawed shredded hashbrowns completely dry with paper towels to remove any residual moisture, spread them evenly into the bottom of the dish, and bake uncovered for 15 minutes to let the surface starch set and crisp slightly.

While the potatoes par-bake, heat a large skillet over medium-high heat. Drop in the ground pork sausage and diced yellow onion, cooking for 6 to 8 minutes while breaking the meat into small, uniform crumbles with a wooden spoon until the pork is thoroughly browned and the onions are translucent.

Tilt the skillet slightly to drain away any heavy excess grease, leaving just a thin coat of flavorful fats to gloss the meat, then pull the pan from the burner.

In a large mixing bowl, combine the condensed cream of chicken soup, sour cream, melted unsalted butter, garlic powder, paprika, and exactly 1 ½ cups of the shredded sharp cheddar cheese, whisking firmly until a smooth, thick binder forms.

Add the browned sausage and onions, along with the par-baked hashbrowns, straight into the bowl with the cream mixture, tossing gently with a large spatula until the ingredients are uniformly suspended in the dairy base.

Transfer the mixture back into the 9×13-inch baking dish, smoothing the surface into a flat, level sheet. Reduce the oven temperature to 350°F, slide the pan onto the middle rack, and bake uncovered for 25 minutes until the edges are bubbling violently.

Carefully slide the hot dish out, blanket the top uniformly with the remaining ½ cup of shredded cheddar cheese, and return to the oven for an additional 5 minutes until the cheese is entirely liquefied, golden, and melted. Let the casserole rest on the counter for 5 to 10 minutes to allow the starches and cheese lipids to stabilize and tighten before scooping into deep squares.