Make the Meat Filling:

• Add the oil to a large skillet and place it over medium-high heat for 2 minutes. Add the onions. Cook 5 minutes, stirring occasionally.
• Add the ground beef (or ground lamb) to the skillet and break it apart with a wooden spoon. Add the parsley, rosemary, thyme, salt, and and pepper. Stir well. Cook for 6-8 minutes, until the meat is browned, stirring occasionally.
• Add the Worcestershire sauce and garlic. Stir to combine. Cook for 1 minute.
• Add the flour and tomato paste. Stir until well incorporated and no clumps of tomato paste remain.
• Add the broth, frozen peas and carrots, and frozen corn. Bring the liquid to a boil then reduce to simmer. Simmer for 5 minutes, stirring occasionally.
• Set the meat mixture aside. Preheat oven to 400°F.

Make the potato topping:

• Place the potatoes in a large pot. Cover the potatoes with water. Bring the water to a boil. Reduce to a simmer. Cook until potatoes are fork tender, 10-15 minutes.
• Drain the potatoes in a colander. Return the potatoes to the hot pot. Let the potatoes rest in the hot pot for 1 minute to evaporate any remaining liquid.
• Add butter, half & half, garlic powder, salt, and pepper. Mash the potatoes and stir until all the ingredients are mixed together.
• Add the parmesan cheese to the potatoes. Stir until well combined.

Assemble the casserole:

• Pour the meat mixture into a 9 x 9 (or 7 x 11) inch baking dish. Spread it out into an even layer. Spoon the mashed potatoes on top of the meat. Carefully spread into an even layer.
• If the baking dish looks very full, place it on a rimmed baking sheet so that the filling doesn’t bubble over into your oven. Bake uncovered for 25-30 minutes.** Cool for 15 minutes before serving.