During the Second World War, food, and especially meat, was rationed in the UK. People were encouraged to grow their own vegetables in their gardens or allotments, and homity pie is a recipe that emerged at that time. The veggies - leeks, potatoes, onions - are very easy to grow in the British climate. After the war, homity pie kind of faded away, but re-emerged as a staple on the menu of Cranks Vegetarian Restaurant in London in the Sixties. It's a really tasty dish, and quite easy to make.
A large knob of butter and the same amount of oil for sautéeing.