Preheat the oven to 170°C and heat the grill or a griddle pan to hot.
Score the pork chops and cut across the fat on the sides to prevent curling.
Rub the halved garlic clove over both sides of each chop and then discard the clove.
Brush the chops with olive oil, season, and brown quickly on both sides under the grill or on the griddle.
Place thyme, rosemary, bay leaves, and fennel seeds in a single layer in an ovenproof dish.
Lay the pork on the herbs, cover with foil, and bake for 40 to 45 minutes.
Finely chop the remaining garlic and mix with parsley and orange zest for the gremolata.
Cut the leeks into 5cm lengths and shred them into fine rings.
Melt butter in a pan, add leeks and orange juice, and season with salt and pepper.
Cover and cook gently for 10 minutes, then uncover and boil off watery juices.
Stir in flour, then gradually add milk and orange zest while stirring until thick.
Add lemon juice and adjust seasoning.
Reheat the sauce gently while stirring frequently before serving.
Discard excess pork fat, spoon leeks onto the plate, top with a chop, and sprinkle with gremolata.