Preheat oven to 350 degrees F.
Cook the ground beef in a skillet over medium high heat. After cooking for for approximately 7 minutes add the diced onions, worcestershire sauce, garlic powder, 1 teaspoon of salt, and ½ teaspoon of pepper. Continue to cook the ground beef for 3 minutes, or until ground beef is cooked through.
Transfer the ground beef to a strainer and let the excess fat drain out before placing the beef back in the pan.
Add the cream cheese to the ground beef and heat over medium low heat until the cream cheese has melted and coats the beef.
Remove the mixture from the heat and stir in the dill relish.
Scoop the beef mixture into an 11x7 inch casserole dish and set aside.
In a small bowl whisk together eggs, heavy cream, remaining 1 teaspoon of salt, and ½ teaspoon of pepper.
Pour the egg mixture over the ground beef gently shaking the casserole dish so the egg mixture is evenly distributed.
Top with the grated cheese.
Place the dish in the oven to bake for 30 minutes or until the casserole is set.
While the casserole bakes make your Big Mac sauce by whisking all of the ingredients together in a small bowl.
When the casserole comes out of the oven drizzle it with the Big Mac sauce before serving.