Shepherd's pie, cottage pie, or hachis Parmentier is a dish consisting of cooked minced meat topped with mashed potato. Its defining ingredients are red meat and onions in gravy or sauce, with a topping of mashed potato. Common variants include adding vegetables to the filling and topping the dish with cheese.
Bring a pot of water to the boil and then drop in the potatoes. Boil for 15 minutes or until the potatoes are tender. Drain and then add the butter. Mash the potatoes until all lumps are removed and set aside.
Place the lamb in a large pot or casserole dish with a little oil and cook until nicely browned. Drain to remove any excess fat and then return to the pot.
Place the pot over a medium heat and add the white wine. Heat until reduced by half then add the vegetables and cook until they are softened but retain their crunch.
Add the stock and reduce until the meat has absorbed all the liquid. Add more stock if the pie mix is a little dry. Season with salt, pepper and thyme and stir in the ketchup and Worcestershire sauce.
Mix in 2 egg yolks to the mash - this will give the mash topping a glossy finish - and then spoon into a piping bag. Pipe the mash on top of the pie filling until completely covered.
Place the pot or dish in an oven set to 200°C/gas mark 6 and cook for around 30 minutes, or until golden brown and bubbling. Serve immediately.