Heat oil in a wide based pot over high head until nearly smoking. Season beef with salt and pepper. Crumble beef around pot using the entire surface area. Use a whisk to break the chunks of beef down. Remove ground beef from the pot and strain fat once nicely browned.

Using half of the strained fat, sauté the onions, garlic, celery, carrot, and rutabaga in the same pot until softened.

Add the tomato paste to the vegetable mixture, and continue cooking for 2 minutes.

Add the ground beef back to pot and deglaze with beer. When the beer is reduced by half, add beef stock, soy sauce, Worcestershire sauce, rosemary and thyme. (If you don’t want to use soy sauce, adjust taste with stock and salt). Bring to a boil and let simmer for 30 minutes. At this point, test the seasoning and add salt and pepper to taste.

In a separate bowl, mix together cornstarch and water, and add to filling to thicken it.

Add the frozen peas and corn, if using.

Check seasoning one more time and adjust to your taste. Pour filling into a deep, heavy bottomed tray and refrigerate for approximately 30 minutes, or until firm.

In a pot, cover potatoes with water and season with salt. Taste the water. If you season your potatoes nicely during cooking, you will get a far better flavour than seasoning after they are cooked and mashed. Adjust the salt to your taste. Place over high heat. When the potatoes boil, turn heat down to a simmer.

When you can pierce the potato all the way through with a skewer or small knife, strain in a colander. Mash the potatoes until smooth.

Add butter until fully incorporated, then follow with sour cream and mustard. Add egg yolk (to help get a nice, golden and crispy top while it bakes).