Hash Brown Casserole

Ingredients

• 1 tablespoon unsalted butter, at room temperature
• One 16-ounce bag frozen shredded hash brown potatoes, thawed
• 8 ounces sharp yellow Cheddar, shredded (about 4 cups)
• 1/2 cup sour cream, plus more for garnish
• 1 medium yellow onion, coarsely grated
• 1 large egg
• 1 1/2 teaspoons sweet paprika
• 1/4 teaspoon cayenne
• 1/4 cup plus 2 tablespoons chopped fresh chives
• Kosher salt and freshly ground black pepper