The meat is prepared by dicing or mincing, and frying with chopped onions, seasoning, and dripping (from the roast) or stock. In the UK, Oxo cubes are a popular form of stock for this dish. Other ingredients can include garlic, chopped carrots, peas or other vegetables, mushrooms, herbs (such as thyme and parsley), tomato purée, and wine. A quick version can be made using canned oxtail soup.
The meat is laid in a dish and covered with mashed potato, to which milk, butter or dripping may be added. The upper surface of the mashed potato may be scored with a fork or, for a decorative effect, it may be piped. The pie is then baked in the oven, making the top surface golden and crisp. Grated cheese can be sprinkled on top prior to baking.
Cottage pie and shepherd's pie are traditional methods for using leftover roasted meat, either beef or mutton, with mashed potato as a convenient pie crust. In early recipes, the pie dish was lined with mashed potato as well as having a mashed potato crust on top.
The use of previously uncooked meat is a recent adaptation, suited to the techniques of commercial food processing companies.
Early cookery writers did not use the terms "cottage pie" and "shepherd's pie" and the terms did not appear in recipe books until the late part of the 19th century. From that time, the terms have been used interchangeably, although there is a popular tendency for "shepherd's pie" to be used when the meat is mutton or lamb.
The term "cottage pie" is known to have been in use by 1791 but it is not known to what type of dish it then referred.