2. In a large skillet over medium heat, heat the oil. Cook all the vegetables, stirring constantly, for 1 minute. Add the beef, Worcestershire sauce, ketchup, thyme, salt, and pepper. Cook, stirring, 1 minute more.
3. Add the cooking juices (up to 1 cup) and turn the heat to high. Bring the mixture to a boil. Taste for seasoning and add more salt and pepper, if you like. Transfer to the baking dish.
4. With a rubber spatula spread the mashed potatoes over the meat to cover it completely. Dot with butter.
5. Bake the pie for 30 minutes or until the potatoes are browned and the meat mixture is bubbling at the edges. Debra Samuels