Peel the potatoes and chop into fairly large pieces. Rinse in cold water.
Add the potatoes to a large pot, cover with chicken stock, and add sea salt, rosemary, thyme, and garlic. Bring to a boil.
Once boiling, reduce heat to a gentle simmer and cook for ~15 minutes or until fork tender.
Carefully strain the potatoes and leave to dry on a rack for at least 30 minutes, or up to overnight in the fridge.
Preheat the oven to 200°C. Add 250g duck fat to a large baking tray and place in the oven for 10 minutes to heat up.
Carefully add the potatoes to the hot tray, coating them in the fat. Bake for 30 minutes.
Flip the potatoes and bake for another 30 minutes, basting where possible.
Chop up fresh rosemary, thyme, and garlic. Mix with a few tablespoons of olive oil.
Remove the potatoes from the oven and pour the garlic and herb mixture over them, tossing to coat.
Return the potatoes to the oven for a final 15 minutes.
Remove the potatoes and season with the rosemary salt (made by grinding rosemary and sea salt in a pestle and mortar).
