- 1 1/2 pounds Russet potatoes, peeled and cubed
- 1 teaspoon salt, plus more to taste
- 4 tablespoons (1/2 stick) butter
- 1/4 cup cream
- 1/4 cup milk, plus more as needed
- ground white pepper
- 1 egg yolk
- 1 tablespoon olive oil
- 1 close garlic, very finely chopped
- 1 pound ground beef
- salt and freshly ground black pepper to taste
- 2 medium carrots, peeled and diced
- 2 teaspoons fresh thyme leaves
- 6 oz tomato paste
- 1 leek, halved lengthwise, rinsed well and sliced
- 1 tablespoon melted butter
For the potato topping, combine potatoes and 1 teaspoon salt in a saucepan with enough cold water to cover by 1 inch. Bring to a boil, lower heat and simmer until potatoes are tender when pierced with a fork. Drain, return potatoes to pan and place back on the heat just long enough for excess water to evaporate. Transfer to a mixing bowl. Add butter, cream and milk and mash. Season to taste with salt and white pepper, then stir in egg yolk. Using an electric mixer at medium speed, whip the mixture until light and fluffy, adding small amounts of milk as needed for a smooth consistency. Set aside.
Preheat over to 400 degrees F and generously butter a 9-inch pie platter or 4 individual casserole dishes.
For the filling, heat oil in a large pan over medium-high heat. Add garlic and cook just until fragrant, about 1 minute. Add ground beef and season with salt and pepper. Cook, breaking up beef with a wooden spoon, until nicely brown, 6 to 8 minutes. Carefully drain excess fat from the pan, lower the heat to medium and add carrots and thyme. Cook until carrots are crisp-tender, about 5 minutes. Stir in Guinness, raise the heat to medium-high and cook, stirring often, until about half the liquid has evaporated, 2 to 3 minutes. Add tomato paste and leeks and cook until leeks soften and the filling has thickened, about two minutes longer. Transfer filling to the prepared pie plate.
Spoon potatoes over the filling as evenly as possible. Use a rubber spatula to smooth the potatoes evenly to cover. Brush the top with melted butter. Bake for 25 minutes or until the potatoes develop a pale golden crust. Let sit 5 minutes before serving.