Preheat your oven to 400°F (200°C). Scrub the russet potatoes clean, then poke a few holes in them with a fork.

Bake directly on the oven rack for about 1 hour until tender when pierced with a knife. Let them cool completely.

Once cool, peel the potatoes carefully and shred them using a box grater or food processor.

In a large mixing bowl, combine shredded potatoes, chopped yellow onion, half of the sharp cheddar cheese, garlic powder, sour cream, salt, and black pepper. Mix well until evenly combined.

Grease a 9x9-inch baking dish with butter or cooking spray. Transfer the potato mixture into the dish and spread it out evenly. Dot the top with small pieces of unsalted butter.

Sprinkle the remaining cheddar cheese over the top of the potato mixture, ensuring it’s evenly distributed.

Reduce the oven temperature to 375°F (190°C). Bake for 25-30 minutes or until the top is bubbly and golden brown.

Let it cool slightly before serving. Garnish with fresh parsley or chives if desired.