• Prepare a large pie plate or 8x8 casserole dish with cooking spray.
• Preheat oven to 350F.
• Get the potatoes boiling. In a large pot of boiling water, add the potatoes and cook until very tender. Drain the water and add the buttermilk and 3 tablespoons of the butter. Mash with a masher or you can use a hand mixer if you want the potatoes to be very creamy. Add more buttermilk if the potato mixture seems dry. Fold in the cheese and season with salt and pepper to taste.
• Heat the oil in a skillet or Dutch oven and sauté the leeks and carrots for about 5 minutes, until tender. Remove from the pot and set aside.
• Brown the ground beef in the same pot, breaking it apart until crumbly. Drain off any grease if necessary. You can keep a tiny bit in the pan.
• Add in the tomato paste, Dijon mustard, Worcestershire sauce, and broth and stir until combined. Simmer for 15 minutes to allow the broth to reduce. Season to taste with salt and pepper.
• If the sauce is thin, it’s optional to add 1-2 Tbsp of flour or cornstarch to a tiny bit of water (whisk together), and add back into the sauce to thicken it up. It’s all personal preference. It doesn’t take much to thicken.
• Add the carrot mixture back into the pan and stir together.
• Dump the mixture into a large pie plate or casserole dish. Spread out evenly.
• Spoon the mashed potatoes over the top of the pie, using the back of a large spoon to make pretty swoops (design). Or, the traditional way is to use the back of a fork to create a crosshatch pattern.
• Melt the remaining 1 tablespoon butter and gently brush over the mashed potatoes.
• Bake the pie for about 45 minutes, or until browned and bubbling.
• Sprinkle lightly with fresh chopped parsley and serve with peas and Soda bread.

Tip: Put a baking sheet under the pie to catch any drippings.