Mashed potatoes

1. Chop the potatoes into 2" pieces and put them in a large pot. Cover with water and add the salt. Bring to a boil and continue to boil until the potato is easily pierced with a fork, about 15-20 minutes.
2. When the potatoes are done, drain the water and put them in a big bowl. Add butter, milk, salt, and pepper, then mash them up with hand beaters or a potato masher. If the potatoes are finished before the meat mixture, leave them in a warm spot and cover the bowl with plastic wrap to keep them warm and spreadable.

Beef filling

1. Preheat the oven to 350°F.
2. Warm a high-sided large pan over medium heat. Add the butter and olive oil. Then add the onion, carrots, celery, and garlic. Stir and cook until the onions start to get some color, 7-10 minutes.
3. Push the vegetables to the side and drop pinches of ground beef all over the pan. Season with salt and pepper. Cook, breaking up the beef with a wooden spoon as it browns.
4. When the beef is fully cooked, add the broth and Worcestershire sauce. Stir everything together and bring it to a boil.
5. Combine the cornstarch and water. When the beef mixture boils, quickly stir the cornstarch and water into the pot. The mixture will thicken in a few minutes.
6. Take the beef mixture off the heat and pour it into a casserole dish. Top with the mashed potatoes by dropping large spoonfuls all over the top and gently seal the mash by smoothing it with the back of the spoon all the way to the edges of the dish.
7. Bake for 30 minutes or until the brown gravy starts to bubble up the edges.