Place Roast Pork on a chopping board and with a sharp knife cut through the skin in a criss-cross pattern about 1 inch apart.
In a bowl mix mustard, chopped sage and chopped garlic, using your fingers spread this mix in-between where the pork skin has been sliced.
In a baking tin large enough to hold pork leg place the onion and the pork on top. Sprinkle sea salt over pork generously.
Cook pork in middle oven tray for about 1 hour, then place peeled potatoes around leg of pork and baste with the pork fat juices, season with sea salt.
After a further 20 minutes increase temperature to gas mark 6, 200ºC (400ºF).
The pork needs an average of 20 minutes in the oven per 500 grm, so using a 3 kg pork leg as an example, I would leave the pork in for at least another 4o minutes to ensure it is cooked through and its skin is crackly, if the skin requires a little more time then leave it in for a further 10 minutes.
Take out tray and rest Pork on chopping board a further 30 minutes, this will allow the juices of the pork to distribute better and prepare your vegetables.
Take out your potatoes and place them on a new tray and return to switched of oven, its plenty hot enough to keep them warm till serving.
Boil your carrots, strain them and finish with a nob of butter, and season with salt, black pepper and a small pinch of sugar.
Using the onions from your roasting tray, prepare a gravy, granules is ok as your apple sauce is your main accompaniment to your Pork.
I find it easier to take of crackling first before slicing pork and sharing it our over sliced pork .to do this just put the edge of your knife under pork and slice gently.
Slice pork generously and serve with Roast potatoes, carrots and Apple Sauce, Gravy separately. Enjoy