In a large mixing bowl, add two pounds lean ground beef, 2 shallots, finely chopped, 3/4 cup panko breadcrumbs, 1/4 cup whole milk, 1 large egg, lightly beaten, 1 teaspoon salt, and 1/4 teaspoon black pepper. With a wooden spoon or your hands mix to combine all the ingredients.
Add the beef mixture to the baking dish and press it down.
Top with 4 ½ cups mashed potatoes, 1 cup shredded cheddar cheese, and ¼ cup crumbled cooked bacon. Cover loosely with aluminum foil and cook for 50 minutes.
After 50 minutes, remove the aluminum foil and continue cooking for an additional 10 minutes.
Remove from oven, serve warm, and garnish with 1 teaspoon chopped fresh parsley if desired.