Preheat oven to 250°C. Using a sharp knife, gently score the skin of the leg across in close parallel lines. Make sure you cut all the way through the skin to the meat (keep in mind, the more scores you make the crispier the crackling).
Rub the entire leg with oil and lemon juice and then with the sea salt. Rub well into the scores as this not only seasons the meat, but helps draw out moisture, producing ‘crispy crackling’.
Place the roast in a large roasting pan. Cook uncovered for 30 minutes at the highest heat, then reduce the temperature to 180°C. Continue cooking for approximately 25 minutes / 500g of weight, or 1½ hours.
Once the roast is done, remove from the oven and rest for 20 minutes before carving to serve.