Gravy is where all the flavour of your roast is concentrated. And what better combination of flavours than pork and apple.

Roast the pork, and the potatoes, and all the other good bits.
While the meat is resting…
Sprinkle a tablespoon of flour into the roasting tin and stir to scrape up all the tasty bits from the bottom of the tin. Slowly add apple juice and stock/water, and keep stirring over the heat for a few minutes.
Apple juice
Plain flour
Roasting juices plus stock/water if needed