In a large skillet, heat a tablespoon of oil over medium heat. Add the diced onion and minced garlic, cooking until softened and fragrant, about 2-3 minutes.

Add the ground beef to the skillet, breaking it apart with a spoon as it cooks. Brown the beef for about 5-7 minutes, ensuring it’s fully cooked through.

Stir in the diced carrots, peas, and tomato paste, mixing everything together.

Pour in the beef broth and Worcestershire sauce, then sprinkle in the dried thyme. Season with salt and pepper to taste. Let the mixture simmer for 10-12 minutes, allowing the flavors to meld and the liquid to reduce slightly.

While the beef filling is simmering, bring a pot of salted water to a boil and add the mashed potatoes (if you're using leftovers, simply reheat them in the microwave or on the stove).

Once the potatoes are soft, mash them until smooth and creamy. Season with a pinch of salt and pepper, and if desired, a small knob of butter for extra richness.

Preheat your oven to 400°F (200°C).

Transfer the beef mixture into a greased baking dish, spreading it evenly across the bottom.

Spoon the creamy mashed potatoes over the beef, spreading them into an even layer with a spatula. For a nice golden top, use a fork to create a decorative pattern on the surface.

Place the assembled pie in the preheated oven and bake for 20-25 minutes, or until the top is golden and the edges are bubbling.

Once done, remove from the oven and let it cool for a few minutes before serving.