Step 1

Fill a 7–8 qt. pot 3/4 of the way with water and bring to a boil. Add the potatoes and boil gently until a knife slips in and out of the potato pieces without any resistance (15–20 min).

Step 2

Meanwhile, heat the olive oil in a skillet over medium heat. Add the leeks; sauté until softened, but not brown. Add the garlic. Sauté an additional minute. Add the cabbage; stir to combine. Lid the skillet and reduce heat to medium-low, stirring occasionally, until the cabbage is soft. Remove from heat.

Step 3

When the potatoes are soft, drain well and return to the pot. Add the butter and stir to combine. After the butter has melted, add the sour cream and milk. Mash to desired consistency with a potato masher (don't worry about getting every lump out: you won't notice them with the cabbage). Add the cabbage and leek mixture along with salt and pepper. Mix well and taste for seasoning, adjusting as necessary.

Step 4

Heat the olive oil in a heavy-bottomed Dutch oven over medium-high heat. Add the lamb and sauté, stirring and breaking up any clumps, until browned, 3–5 minutes. Drain and set aside.

Step 5

Add the onions, carrots, and celery to the pot. Reduce heat to medium. Sauté until the onions are translucent and the vegetables are soft, 8-10 minutes. Add the garlic; sauté an additional minute. Sprinkle the flour over the vegetables; stir to combine and sauté for 1 minute. Add in the tomato paste, rosemary, thyme, and fish sauce. Sauté for an additional minute. Return the lamb to the pot and add the Guinness and beef broth.

Step 6

Simmer uncovered, stirring occasionally, until the liquid has reduced down to a thick gravy, 15-20 minutes. Remove from heat. Stir in the frozen peas and corn kernels.

Step 7

Preheat oven to 400º. Pour the filling into a 9x13 baking dish. Spoon the colcannon on top of the filling, beginning at the edges. Use a silicone or rubber spatula to spread the colcannon over the filling and out to the sides of the dish to make a seal (this keeps the filling from bubbling up and out).

Step 8

Place the baking dish onto a baking sheet lined with aluminum foil. Bake for ~25 minutes, or until the colcannon is golden-brown. Let cool for at least 10 minutes. Sprinkle with sliced scallions and parsley; serve.