Shepherd's Pie is truly the ultimate comfort food. What other dish gives you your meat and potatoes all in one pot? The filling is savory and loaded with vegetables and the whipped potatoes bake to perfection in the oven. Beef can be substituted for the ground lamb, but then it's called Cottage Pie. We love lamb! It works perfectly in this iconic dish.
Melt the 2 tbsp butter in a large skillet over medium-high heat.
Add the leeks, onion, and carrots and cook until softened, about 5 minutes. Add the garlic and cook for about another minute.
Add the lamb to the skillet, breaking it up with the back of a wooden spoon. Cook until just no longer pink. If too much fat has rendered, carefully tip the skillet to one side and use a large spoon to scoop out most of the grease.
Season with salt and pepper.
Sprinkle the flour over the meat and then add the tomato paste, stirring to incorporate into the meat mixture, about 1 minute.
Whisk in the stock and Worcestershire sauce and then add the thyme, rosemary and nutmeg.
Increase heat and bring to a boil. Lower the heat and simmer for 10 minutes, until sauce has thickened somewhat.
Meanwhile, place the potatoes into a large pot and cover with salted water (about 2 tbsp of salt). Bring to a boil over high heat.
Simmer for 20 minutes, or until potatoes are cooked and easily pierced with the tip of a sharp knife.
Drain and add the potatoes to a large bowl. Add the half-and-half, butter (6 tbsp), salt and pepper, and mash with hand mixer, or potato masher until smooth. Taste and add more salt, if necessary.
Pre-heat oven to 375°F.
Stir in the corn and peas into the meat mixture.
Layer the meat mixture into a 2-quart baking dish (11"x7" works well).
Top with the potatoes, spreading them so they touch (and seal) the sides of the dish and are even all over. Use the back of a spoon to smooth and create swirls and little wisps.
Bake for 30 minutes, or until bubbling and the wisps have slightly browned. If you desire the potatoes to brown a little more, place under the broiler (on high) for about 1 to 2 minutes. (Keep an eye on them as broilers vary).
Remove from oven and let rest for 10 minutes on a rack. Garnish with chopped parsley on top, if desired.