Combine beef broth, Worcestershire sauce, tomato paste, and Dijon mustard; whisk until well blended. Set aside. (See Tip 3)
Brown ground beef in a large non-stick skillet. Drain in a colander and rinse well with hot water to remove as much fat as possible. Wipe the skillet with a paper towel and place over medium heat. (See Tip 3)
Heat olive oil or butter in a skillet over medium heat. Add onion and carrots; cook until tender, about 5 minutes. Add ground beef, flour, salt, and pepper. Stir to combine. Cook for several minutes. Add beef broth mixture; cook, constantly stirring over medium heat, until bubbly and thickened. Cover and continue cooking over medium-low heat for 45 minutes or until the meat and vegetables are tender. (See Tip 4)
Add the frozen peas and stir to combine all ingredients. (See Tip 5)
Spoon into a buttered casserole dish(es). Pipe mashed potatoes over the meat mixture. May be prepared in advance up to this point. (See Tip 6)
Bake at 375ºF for 25 to 30 minutes, or until the top of the potatoes is lightly browned and the mixture is bubbly. Yield: 8 servings. (See Tip 7)
Mashed Potatoes
Place potatoes and 1 Tablespoon salt in a large saucepan. Cover potatoes with water; bring to a boil over high heat. Reduce heat to medium and continue cooking until potatoes are very soft, about 20 minutes; drain well in a colander. Return potatoes to the pan and heat over medium heat for several minutes to dry out. Add butter and cheese. Mix well. Add milk; beat with an electric mixer until potatoes are smooth and creamy. Add salt and pepper to taste. Allow potatoes to cool slightly.
Transfer the potatoes to a piping bag fitted with a large (1M) star tip, and pipe the potatoes in swirls on top of the meat mixture.
Video
Tips/Notes
May use chicken broth rather than beef broth.
I used 90% ground beef, but you could also use 85% ground beef.
If using Bisto, add it to the broth mixture.
I know rinsing the cooked ground beef removes some of the flavor. However, it also removes most of the grease. You could certainly skip this step.
I like to cover the pan with paper towels before putting the lid on. The reason is that the paper towel traps the condensate and keeps it from falling back into the meat mixture. This keeps the meat mixture nice and thick.
I like to wait until the end to add the frozen peas because I don't like them overcooked.
Refrigerate the Cottage Pie that you're going to eat, and freeze the others. I thaw the frozen Cottage Pies in the microwave before putting them in the oven.
The leftovers are just as good the next day. I generally heat the leftovers in the microwave.