For the pork chops, season the chops with the salt and scatter the black pepper over them, pressing it firmly into the chops on each side.
On a medium heat, in a large frying pan, heat the butter until foaming, but without letting it burn.
Raise the heat to medium high, lay the chops in the foaming butter and cook for four minutes on each side for medium.
Transfer the chops to a warm plate with tongs. Pour 100ml/3½fl oz cold water into the hot pan. There will be a lot of sizzling, and the water and butter will create an emulsion. Scrape the base of the pan with a wooden spoon to release the caramelised residue, which will give taste and colour to the juice. Continue to heat for a minute or so until the liquid reduces in volume to a rich sauce.
For the sauté potatoes, blanch the diced potatoes in a pan of boiling water for 30 seconds, then drain in a colander and allow the steam to escape for a minute or two. (Of course you can cook the potatoes from raw, but they may brown too quickly as they have a high starch content. By blanching them you are neutralising the starches, giving the potato a better texture and colour.)
On a high heat, in a large frying pan, gently fry the diced potatoes in the oil, season with salt and pepper and cook for 4-5 minutes stirring every minute until golden-brown.
For the persillade, mix together all the ingredients in a small bowl.
Reduce the heat of the potatoes, add the butter and two-thirds of the persillade. Taste and adjust the seasoning if necessary.
To serve, pour the juices from the deglazed chop pan onto the steaks and serve with the sautéed potatoes, crisp sage leaves and Dijon mustard.