Place peeled and quartered potatoes in a large pot of cold salted water and bring to a boil over high heat. While the potatoes cook, prepare all your other ingredients: dice the onion finely, mince the garlic, dice the carrots into 1/2-inch pieces, and chop the fresh parsley. Having everything prepped and ready before the meat cooking begins will keep your workflow smooth and prevent any ingredients from overcooking or getting cold.

Heat olive oil in a large skillet over medium-high heat and add the diced onion and minced garlic, cooking for about 2-3 minutes until softened and fragrant. Add the ground beef, breaking it up as it cooks, and season with salt and pepper. Brown the meat thoroughly for about 5-7 minutes, stirring occasionally—this creates deeply flavorful fond on the bottom of the pan that will add richness to your sauce. I find that taking the extra time to properly brown the meat makes a real difference in the final depth of flavor.

Add the diced carrots and bay leaf to the browned beef mixture and cook for 5 minutes to begin softening the carrots and infuse the bay leaf's flavor. Push the meat mixture slightly to the side of the pan and sprinkle the flour over the empty space, stirring it into the pan drippings for about 1 minute to cook out the raw flour taste and create a flavorful roux base. Pour in the hot water and tomato paste, stirring everything together until well combined and the flour is fully incorporated into a smooth sauce. Add the Worcestershire sauce and stir well. The sauce should be thick but pourable at this point.

Check that your potatoes are fork-tender (they should be done by now), drain them well in a colander, and return them to the pot. Preheat your oven to 375°F. Immediately mash the hot potatoes with the butter, cream, and milk, stirring until creamy and smooth—working with hot potatoes helps them absorb the dairy better and creates a fluffier texture. Season with nutmeg, salt, and pepper to taste. I like using freshly ground nutmeg because it has so much more aromatic intensity than pre-ground, and just a teaspoon adds warmth without making the potatoes taste spiced.

Spray a 9x13-inch casserole dish with vegetable oil spray. Transfer the meat sauce from Step 3 to the prepared dish, spreading it in an even layer. Remove and discard the bay leaf. Scatter the frozen green beans over the meat mixture in an even layer—you don't need to thaw them first, they'll cook perfectly in the oven. Spread the mashed potato mixture from Step 4 evenly over the green beans, using a spatula to create a smooth, even layer that reaches the edges of the dish. This helps the potatoes brown evenly and prevents any filling from bubbling up the sides.

Place the assembled shepherd's pie in the preheated 375°F oven and bake for 30 minutes, until the top is golden brown and the filling is bubbling slightly at the edges. Remove from the oven and let rest for 5 minutes—this allows the layers to set slightly and makes serving cleaner. Top with the fresh chopped parsley for color and a fresh flavor contrast before serving. The parsley adds brightness to the rich, comforting dish.