This classic comfort food is made even easier with the help of a food processor. Pulse together potatoes, butter, and milk to make the mashed potato topping. In the Dutch oven, sauté onions, carrots, and celery until tender, then add ground beef and cook until browned. Add canned tomatoes, beef broth, and frozen peas, then simmer until the flavors have melded together. Top with the mashed potatoes and bake until golden brown.
