Quarter the potatoes and add to the stock pot. Cover with water by about an inch. Bring to boil and then reduce heat until the water is simmering.

Cook the potatoes about 15 - 20 minutes until slightly soft in the middle. They should give when squeezed.

Preheat the oven to 300°F.

While the potatoes are cooking, place the olive oil in a medium sauce pan over medium heat. Add the onions and cook for about 3 minutes until they begin to soften.

Add the ground beef and cook, stirring frequently, until browned.

Sprinkle the cornstarch over the ground beef and stir in. Add the carrot, celery, tomato paste, salt, Worcestershire sauce and beef stock. Stir, cover and place the pot in the oven.

When the potatoes are done, remove from heat and drain the water. Pass the potatoes through a ricer or mash gently with a fork until smooth.

Add butter, buttermilk, milk and 1/8 salt and stir in. Add ground black pepper to taste.

After an hour of cooking in the oven, remove the beef and divide between two bowls (you can make this in one pyrex dish also). Top with the potatoes and return to the oven. Bake for about 10 minutes and serve.