Preheat oven to 350°F and spray 13x9-inch baking dish with nonstick cooking spray.
Place the potatoes in a large saucepan set over medium-high heat, and cover them with cold water. Bring the water to a boil and reduce the heat to low. Cook, uncovered 8-10 minutes or until the potatoes are just fork tender. Drain the potatoes and place them in the prepared baking dish.
3 pounds Yukon Gold potatoes
Pour the melted butter over the potatoes.
¼ cup unsalted butter
While the potatoes cook, crumble the sausage in a large skillet set over medium heat. Add the chopped onion and cook until the onion is translucent and the sausage is cooked through. Transfer the sausage/onion mixture to a paper towel-lined plate and dab the top of the mixture with another paper towel.
1 pound bulk hot pork sausage, 1 yellow onion
Spread the sausage/onion mixture over the potatoes and gently toss the mixture together.
Top with cheese and bake, uncovered, at 350°F for 7-10 minutes or until the cheese is melted.
2 cups freshly shredded cheese
Garnish with chopped parsley, if desired, and serve.
2 tablespoons chopped fresh parsley