Step 1

Start with the mashed potatoes topping. Peel and chop the 3 pounds Yukon Gold potatoes into big chunks. Place them into a large soup pot, covered with water. and stir in 1 tablespoon kosher salt.

Step 2

Place the pot over high heat and bring to a boil. Once boiling, reduce the heat to a simmer and cook until the potatoes are fork-tender, about 15 minutes.

Step 3

While the potatoes are cooking, make the filling. Heat the 1 tablespoon olive oil in a pan over medium heat. Sauté the 1 sweet onion, 2 sticks celery, 2 medium carrots and 3-4 cloves garlic for 5 minutes.

Step 4

Add the 1 pound lean ground beef and cook, mincing the meat with the wooden spoon.

Step 5

Once the meat starts to brown, sprinkle it with the 2 tablespoons cornstarch, 1 teaspoon dried thyme and season with Kosher salt and pepper. About 3-5 minutes.

Step 6

Add the 2/3 cup chicken broth, 2/3 cup tomato passata and 1 cup frozen peas. Stir well to combine and simmer the sauce until it begins to thicken, around 5-7 minutes.

Step 7

Transfer the sauce to an oven-safe dish and preheat the oven to 450F.

Step 8

To make the mashed potatoes, drain the cooked potatoes and mash with the 2 tablespoons olive oil, 1/2 cup plain Greek yogurt or sour cream, or sour cream, and 1/2 milk of choice. Season, if needed.

Step 9

Spoon the mashed potatoes over the meat mixture into the dish.

Step 10

Bake for 30-35 minutes, or until bubbly. Broil for 2-4 minutes to give a nice charred top.