• Begin by preheating the oven to 350 degrees.
• Melt the butter (or use olive oil) in a pan over medium heat and add the onion, carrots, celery, and garlic; cook 5-7 minutes until the vegetables begin to soften.
• Add the beef and cook, breaking up the large clumps, until it’s no longer pink. Remove any excess beef fat.
• Stir in the tomato paste, flour, Worcestershire sauce, Italian seasoning.
• Add in beef stock, salt, black pepper, and frozen peas to the meat mixture.
• Cook a few minutes more to warm up the peas and allow the flavors to merge.
• Taste and adjust for salt if necessary. Transfer filling to an 8×11 casserole dish. Set aside.

Make The Mashed Potato Topping

• Add peeled, chopped potatoes to heavily salted boiling water and cook until the potatoes are fork tender.
• Drain the water and add the potatoes back to the pot. Add the butter, cream, salt, and pepper; mash together until you have a really smooth consistency.
• Taste and adjust for salt if necessary.
• Spread the fluffy mashed potatoes over your meat and vegetable filling in your baking dish.
• Fluff the potatoes lightly with a fork (to create peaks that will brown in the oven) and sprinkle with freshly grated parmesan cheese.
• Place in the preheated oven for 20 minutes until the pie is warmed through and the top is evenly golden brown. You may need to turn your broiler on for a few minutes at the end to achieve really nice browning. Watch the pie carefully at this stage to ensure it doesn’t burn.