Preheat your oven to 400°F (200°C). In a large bowl, mix the refrigerated shredded hash browns with the melted butter and kosher salt. Press the mixture firmly into the bottom and slightly up the sides of a greased 9x13-inch dish. Bake uncovered for 20-25 minutes until golden-brown, visibly crispy, and browned on the edges. Remove from oven and immediately lower temperature to 375°F (190°C).

While the crust is baking, cook the ground breakfast sausage in a heavy skillet over medium-high heat. Break it apart into crumbles and cook until no pink remains. Use a slotted spoon to transfer the meat to a paper towel-lined plate to drain excess grease.

In a clean mixing bowl, vigorously whisk together the eggs, whole milk, and black pepper for at least 60 seconds until aerated and pale yellow.

Spread the cooked, crumbled sausage meat in an even, substantial layer over the baked hashbrown crust. Evenly scatter the cold cream cheese cubes across the sausage to create pockets of white cream cheese. Gently pour the fluffy egg mixture over the top.

Bake uncovered at 375°F (190°C) for 25-30 minutes, or until the center is set and no longer liquid.

Remove the casserole briefly and cover the entire top surface with the shredded sharp cheddar cheese. Switch your oven to Broil (High). Broil the casserole for 1-2 minutes, watching closely, until the cheese is melted, bubbly, deeply browned, and slightly charred in spots.

Allow the casserole to rest for 10-15 minutes. Slice into thick, square slices. Serve on a white ceramic plate and garnish each slice with a single, fresh sprig of thyme.