Preheat oven to 200C. Place potatoes into a large saucepan, add salt and cover with water. Bring to the boil, then simmer until par-boiled, about 12 minutes.
Drain potatoes well, return to the saucepan, place over low heat to steam dry.
Meanwhile, place duck fat into a large deep metal roasting pan and allow to melt and heat in the oven for 8 minutes.
Shake the potatoes in the saucepan to roughen up the surface. Place each potato on a chopping board and gently squash with the back of a fork.
Carefully place the potatoes in a singular layer in the roasting pan, turning to coat in the duck fat.
Roast for 45-60 minutes or until crunchy and golden, occasionally turning the potatoes for even cooking.
Meanwhile, place the sea salt in a small bowl and rub the chopped herbs into the salt to release their aromatic oils.
Serve potatoes liberally seasoned with the herb salt.
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