Preheat the oven to 450°F. Spray a 12 cup muffin tin with cooking spray. Set aside.
If using frozen shredded hash browns: Thaw completely before adding to the mixing bowl.
Mix shredded potatoes, egg whites, Parmesan cheese, salt, onion powder, garlic powder and pepper together.
Scoop 1/4 cup of potato mixture into each muffin cup. Use a small glass to press the potato mixture firmly into the bottom and up the sides of each cup.
Alternately, drizzle each with melted butter.
Bake for 22-25 minutes or until cooked through and golden. Sprinkle with shredded cheese in the last few minutes of baking.
Remove from the oven and gently run a knife or an offset spatula around each nest to loosen the edges. Allow to cool in the pan for around 2 minutes before attempting to remove.
To assemble: Top with sour cream and crumbled bacon. Garnish with finely chopped parsley or chives. Serve warm.