Fill a stockpot with the potatoes, cover with cold water, and mix in 2 tablespoons of kosher salt. Bring to a boil and cook until fork tender (about 25-30 minutes).

Rice the potatoes in a large bowl. Combine with the heavy cream, melted butter, and 1 cup of parmesan cheese. Taste test the potatoes and season very well with salt and pepper to taste. Once satisfied with the taste, mix the egg yolks into the potatoes.

Preheat oven to 400f and set one rack in the middle and one towards the top ⅓ of the oven.

While the potatoes are boiling make the filling. Heat a large heavy pan or pot to medium-high heat then add the lamb.

Cook until well browned (about 7-10 minutes), then break up the lamb with a wooden spoon or meat masher. Next, add the carrots, onions, and celery along with a pinch of salt. Saute until the veggies are soft (about 5-7 minutes) then add the garlic and cook for another 1-2 minutes or until fragrant.

Add the tomato paste, stir, and cook for 3 minutes. Next, add the Guinness and turn the heat to high. With a wooden spoon scrape the bottom of the pot to remove all of the brown bits. Cook until the liquid has almost completely evaporated (about 3-4 minutes).

Turn the heat down to medium and add the flour. Cook for 1-2 minutes or until there is no white flour remaining in the pan. Add the beef stock, thyme, rosemary, peas, and Worcestershire sauce. Bring to a boil. Once boiling, lower the heat to a simmer and cook until the liquid has reduced by half.

Taste test the filling and adjust salt, pepper, thyme, or rosemary if required.

Add the filling to a 9x13" baking dish. Spread the mashed potatoes on the top and with a fork or spoon fluff the potatoes making mounds or points. Sprinkle the remaining ¼ cup of grated parmesan.

Bake for 20 minutes in the center of the oven. Move the dish towards the top of the oven and broil for 1-3 minutes or until well browned but not burnt. Watch carefully! Let the shepherd's pie sit for 10 minutes before eating so that it can settle. Enjoy!