This Traditional Irish Shepherd's Pie is a classic comfort food perfect for St. Patricks Day or any special occasion. The light sweetness of the ground lamb and vegetable filling is perfectly balanced with the savoriness of the fluffy mashed potatoes. This casserole dish is sure to be a hit for your next gathering.
Scrub the potatoes under running water with a vegetable brush to remove any dirt or debris. Peel and cut the potatoes into 1 to 2-inch thick chunks.
In a large stockpot, cover the potatoes with cold water and heat to a boil. Once boiling, turn the heat down to a simmer. Cook until the potatoes are tender in the middle, 20 to 30 minutes. Mine took about 25 minutes to cook through. Use a paring knife to check doneness by inserting the knife into the potatoes. When there is little resistance when inserting the knife, they are done.
Drain the potatoes in a colander and rinse under hot water for 10-20 seconds to wash away any excess starch. Place back in the pot.
Add the softened butter and mash thoroughly into the potatoes using a potato masher. Next, add the warm milk, and salt and fold in using a spatula.
make the Lamb Filling
While the potatoes are cooking, heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the diced onion to the skillet and sauté until the onion becomes soft and begins to brown around the edges, 4 to 5 minutes.
Add the minced garlic, rosemary, and thyme to the skillet. Mix into the onion and cook for another minute to release the flavors and aromas of the herbs.
Add the ground lamb and break into small pieces while cooking. Sauté until cooked through, about 8 to 10 minutes. Drain the meat and return to the skillet and sauté for another minute or two.
Sprinkle the 1/2 tsp salt, black pepper, and flour over the lamb and then mix into the meat. Next add the red wine, Worcestershire sauce, soy sauce, and tomato paste to the skillet and mix into the meat. Cook for a few minutes to allow the liquid to reduce.
Add the chicken stock and vegetables to the skillet, mix into the meat, and allow to come to a boil. As soon as the liquid begins to boil, turn the heat down to medium and allow to cook while the liquid reduces and thickens, about 10 minutes. Mix occasionally so that the meat doesn't burn to the bottom of the skillet.
assemble the Shepherd's Pie
Evenly spread the lamb filling on the bottom of a baking dish. Spoon or pipe the mashed potatoes evenly over the lamb. Then, lightly brush the top of the potatoes with the beaten egg and sprinkle the parmesan cheese evenly over the top.
Place the baking dish on the middle rack of a preheated oven and bake for 25 minutes or until the peaks of the potatoes begin to brown.
Remove from the oven and allow to cool for 5 minutes before serving.