Prep Oven & Baking Dish: Preheat your oven to 375°F (190°C). Generously grease a 9x13-inch ceramic or glass baking dish with 1 tablespoon butter or nonstick cooking spray.

Dry the Hash Browns & Toss with Butter: Ensure your shredded hash browns are thawed. Place them between several layers of clean paper towels or a clean kitchen towel and press firmly to extract any excess moisture (this guarantees a fluffy, never-soggy casserole). Transfer dried hash browns to a large mixing bowl and toss with 1/4 cup melted butter until coated.

Whisk the Savory Custard: In a separate mixing bowl, whisk together the 8 eggs, whole milk, sour cream, garlic powder, onion powder, smoked paprika, sea salt, and black pepper until completely smooth and lightly frothy.

Combine Hash Browns, Veggies & Cheese: To the hash browns bowl, add the diced red bell pepper, the white and light green parts of the sliced scallions, 2 cups of shredded sharp cheddar, and 1/2 cup of grated Parmesan. Pour the whisked egg custard over the mixture and fold gently with a spatula until evenly distributed.

Spread & Top with Cheese: Spread the hash brown mixture evenly into the prepared 9x13-inch baking dish. Scatter the reserved 1/2 cup of sharp cheddar cheese evenly across the top to form a golden cheese blanket.

Bake to Golden Bubbly Perfection: Bake uncovered at 375°F (190°C) for 42 to 45 minutes, until the center is set (a knife inserted into the middle comes out clean) and the top is puffed and deeply golden-brown. If you desire extra crispy top edges, broil on HIGH for the final 2 minutes.

Rest, Garnish & Slice: Remove from the oven and let rest on a wire rack for 10 minutes (this allows the egg custard to set completely for clean, neat slices). Scatter the dark green scallion tops and fresh snipped chives over the casserole. Slice into 8 generous squares and serve warm!