How to Make It
Peel the potatoes and cut into chunks. In a large pot, cover the potatoes with warm, salted water, then bring to a boil. Boil until the potatoes are very tender, about 25 minutes. Drain the potatoes, then mash them with the milk, butter, and salt to taste. Reserve the mashed potatoes. Preheat the oven to 500°F.
In a large cast-iron or heavy skillet, heat the oil over medium high heat until hot, then stir in the onion, garlic, carrots, potato, 3/4 teaspoon salt and 1/2 tea-spoon pepper. Cook, stirring occasionally, until golden, 8 to 10 minutes. Stir in the flour and cook, until incorporated, about 2 minutes. Pour in the stock and bring to a boil, then stir in the chicken. Season the filling with salt and pepper to taste. Transfer the filling to a 3-quart baking dish. Spread the potatoes evenly over top of the filling. Bake the shepherd’s pie pot pie until the potatoes are browned in spots and the filling is bubbling, about 15 minutes.