Pork leg: remove any packaging from the pork and leave it uncovered on a plate in the fridge overnight to dry out the skin.
Preheat the oven: preheat the oven to 220°C/ 425°F / Gas Mark 7.
Season: flip the pork so that the meat side is facing up and place it onto a chopping board. Season this side with salt and black pepper. Then sprinkle the garlic powder over the top, followed by the onion powder. Use your fingers to massage this into the meat.
Skin: once you have seasoned the pork, flip it back to skin side up. Fold a piece of paper towel into a square and use this to pat dry the meat.
Olive and salt: next pour olive oil over the surface of the skin and use a basting brush to spread it across the skin. Then sprinkle salt directly onto the oil, ensuring an even coverage.
Oven bake: pour 2 cups of tap water into a rack in roasting tin. Then place the pork leg onto the rack. Oven bake it for 50 minutes at the temperature listed in step 2. After this cooking time is up, reduce the oven temperature to 180°C / 350-375°F / Gas Mark 4-5. Let the pork then cook for 1 hour, then use oven mitts to remove the roasting tray and place it onto a heatproof surface. Insert a thermometer into the thickest part of the meat and ensure that it reads at least 70°C (158°F). Or return to oven and test again after 5-10 minutes. Once the pork has reached this temperature, turn the oven back up to the original cooking temperature of 220°C/ 425°F / Gas Mark 7 and cook it for a final 5 minutes to get the crackling one final hot heat blast. Then use oven mitts to remove the pork and place the roasting tray on a heat proof surface.
Rest: let the pork rest (uncovered) for 15 minutes so that the juices are reabsorbed into the meat.
To serve: when ready, use a carving fork, sharp knife and chopping board to slice the meat and crackling. Then transfer to a serving plate. Serve with potatoes and steamed greens (optional).