Start by peeling your potatoes and cutting them into uniform 3-inch chunks to ensure even cooking. Place them in a large pot, cover with cold water, and add 1 tablespoon of table salt. Bring to a boil and simmer until the potatoes are par-cooked, about 10 minutes. They should be just tender on the outside but still firm in the center.

While the potatoes are simmering, set your oven to preheat at 450°F.

In a small saucepan, gently melt the duck fat over low heat. Add the chopped rosemary to infuse the fat. Keep it on the lowest heat setting just to keep the fat liquid.

Drain the potatoes and let them steam dry for a moment or two. Then, give them a shake in the pot to rough up the edges (this is the secret to creating more surface area for that ultimate crunch). Sprinkle the semolina and kosher salt over the potatoes, and toss.

Carefully take your preheated roasting pan out of the oven and add the infused duck fat. Spread the fat evenly, then add your coated potatoes in a single layer, turning to coat in the fat. Roast in the oven for 20 minutes, then turn the potatoes and continue roasting for another 20-30 minutes. You want them golden.

Once done, transfer the potatoes to a serving dish and sprinkle with sea salt flakes to taste.