Preheat oven to 350 degrees. Spray a 9 inch round or 8x8 inch square casserole dish with coconut oil cooking spray.
Cook the ground beef/chuck with the onion. Drain well.
Spread the beef mixture evenly in the baking dish.
In a mixing bowl, whisk together the seasonings, eggs, and heavy cream. Slowly pour over the beef mixture so it sinks into the meat.
Top casserole with cheese.
Bake for 30 to 35 minutes or until the center is set. Allow the casserole to rest about 5 minutes before slicing.
Serve with cheeseburger toppings like pickles, mustard, lettuce, tomato, bacon, etc.