Preheat the oven to 425°F. Lightly spray a deep 10-inch pie plate or 10-inch oven-safe skillet with nonstick cooking spray.
Place the thawed hash browns in a clean kitchen towel and squeeze firmly to remove excess moisture.
Combine the potatoes with three tablespoons melted butter, beaten egg, one cup shredded cheddar, ¼ teaspoon salt, and ¼ teaspoon black pepper.
Reserve one-third of the potato mixture. Press the remainder firmly into the bottom and sides of the prepared dish.
Bake the crust for 20 to 25 minutes, until lightly golden around the edges.
Meanwhile, brown the ground beef in a large skillet over medium-high heat for six to eight minutes. Drain excess grease and transfer the beef to a plate.
Add the remaining two tablespoons butter and sliced onions to the skillet. Cook over medium heat for eight to ten minutes until soft and lightly browned.
Add the garlic and cook for 30 seconds.
Sprinkle the flour over the onions and cook for one minute.
Gradually whisk in the beef broth. Add Worcestershire sauce, onion powder, garlic powder, thyme, remaining salt, and remaining black pepper.
Simmer for three to five minutes until thickened.
Return the beef to the skillet and simmer for another two minutes.
Reduce the oven temperature to 375°F.
Spoon the beef and onion gravy into the prebaked hash brown crust. Sprinkle with one cup cheddar cheese.
Scatter the reserved hash browns over the top and finish with the remaining ½ cup cheese.
Bake for 25 to 30 minutes until bubbling and golden brown.
Let the pie rest for ten minutes before slicing. Garnish with parsley if desired.