For the Mashed Potato Topping

Put a large pot of well-salted water on to boil. Cook the potatoes at a nice simmer until fork tender. Drain. Return to the pot and allow any excess water to evaporate. Add the butter, milk, 1 ½ teaspoons of kosher salt, and a few turns of black pepper. Mash the potatoes until soft. Stir in the sliced scallions. Taste for seasoning; you may want a little more salt. Set aside.

For the Ground Beef Filling and to Finish

While the potatoes are boiling, heat a large, oven-proof skillet with the oil over medium- to medium-high heat. When the oil shimmers, add the carrots, onion, thyme, bay leaves, mushrooms, garlic, and 1 teaspoon of kosher salt. Cook, stirring frequently, until softened and lightly brown. Add the tomato paste and stir until coated.

Deglaze the skillet with the Worcestershire and red wine, scraping up any browned bits that may have stuck to the skillet. Add the stock. Bring to a simmer and add the ground beef in tablespoon-sized chunks. Let simmer for about 10 minutes. Stir a couple times as the meat cooks to turn the meat and break the beef chunks up a bit.TIP: This may be a good time to see if the potatoes are done.

Use a fork and a small bowl to whisk the cornstarch with a tablespoon of water to make a slurry. Make a well in the beef and vegetable mix. Add the cornstarch slurry and continue to simmer for another minute or two, stirring. The mixture should become thick and stewy, more gravy than soup. If it seems liquid-y, continue to cook for another minute or two.

Turn off the heat. Remove the bay leaves and thyme stems.

Preheat the broiler and set the rack to the upper third. Spoon the mashed potatoes into a gallon bag. Snip one corner and twist the top opening shut. This is your piping bag. Pipe the potatoes evenly over the potatoes. Smooth with a spatula, then use a fork to rake the top of the mashed potatoes.

Broil for around 5 minutes (check often), until the top is golden brown and the juices are bubbling.

Cool 10 minutes before serving.