Preparing the Potatoes:

1. Peel and Cut: Remove the skins from the potatoes and slice them into 3-inch chunks.
2. Preheat Oven: Set your oven to 450°F.

Par Boiling & Roughing Up:

1. Boil Potatoes: Fill a large pot with water, bring to a boil, and add 1 tbsp of kosher salt. Add the potatoes and cook for 10 minutes.
2. Drain: Thoroughly drain the potatoes and shake off any excess water.
3. Steam Dry: Return the potatoes to the dry pot on the stove (turned off) for about 3 minutes to let the steam evaporate and dry out.
4. Rough Up: Sprinkle 1 1/2 tsp of kosher salt and the semolina over the potatoes. Cover the pot with a lid and shake it vigorously 5 to 7 times to rough up the surface.

Roasting:

1. Heat Duck Fat: Place the duck fat in a heavy metal roasting pan (avoid using glass or ceramic because it can shatter at high temperatures). Heat it in the oven for 5 to 7 minutes until the fat is shimmering and slightly smoking.
2. Add Potatoes: Carefully take the pan out of the oven. Quickly add the potatoes to the hot fat, turning them to ensure they are well-coated. Arrange them cut-side down.
3. Roast: Roast the potatoes for 25 minutes. Turn them over, then roast for another 25 minutes until they are a deep golden color and very crunchy.
4. Remove from Oven and Season: Add final seasonings, tossing to coat potatoes thoroughly.
5. Serve: Immediately remove seasoned potatoes from hot roasting pan and place them into a serving dish. Adjust salt and pepper to taste, and serve immediately.