Apply a non-stick cooking spray to a 9x13 baking dish.
In a big frying pan, put the onion and ground beef and cook until the meat is fully cooked.
Cut the potatoes into slices that are about a quarter of an inch thick.
Put a layer of potatoes at the bottom of the baking dish.
Add a little salt and pepper.
Put about one-third of the meat mixture on top and spread it evenly over the potatoes.
Put 1/3 of the grated cheese on top.
Say this two more times, adding one on top of the other.
The final layer should consist of the cheese that is left.
Mix the Cheddar cheese soup mix with milk, evaporated milk, and add salt and pepper if you like.
Put the soup mix on top of the potatoes and beef mix.
Put aluminum foil tightly over the baking pan and place it in the oven.
Cook in the oven for 60 minutes.
Take off the cover and bake for 15 more minutes to make the cheese on top turn golden.
If the potatoes are thicker, you will have to cook the dish for a longer time.
Have fun.