Preheat oven to 400°F (200°C).

In a large skillet, brown hamburger and chopped onions over medium-high heat.

Drain off any excess grease from the skillet.

Transfer the browned hamburger and onion mixture to a deep dish pie plate or casserole dish.

Spread the cooked and drained frozen corn evenly over the meat mixture.

In a separate bowl, combine the thick mashed potatoes with the egg and mix well.

Spread the mashed potato mixture evenly over the corn layer, creating a seal around the edges.

If desired, sprinkle a touch of grated American or Parmesan cheese over the potato topping.

Bake in the preheated oven for approximately 45 minutes, or until the potatoes are slightly browned and the filling is heated through.