The primary ingredient in a traditional steak pie is beef, specifically cuts that are well-suited for slow cooking, such as chuck or stewing steak. The beef is typically marinated and cooked slowly until tender, often with a combination of vegetables like onions, carrots, and celery, and flavored with herbs and spices. The filling is then encased in a pastry shell, which can be shortcrust or puff pastry, ready for baking. Steak pies are a beloved comfort food in many cultures, particularly in the UK, where they are often served with mashed potatoes and gravy, highlighting their hearty and satisfying nature.