Your fish is cooked when you can push the blade of a knife into the flesh with no resistance.
Zest half the lemon with a zester, then juice the lemon. Set aside.
Prepare the leeks by halving them lengthways, then chopping finely.
Melt the butter in the frying pan, then sweat the leeks with a pinch of salt and let them cook for 10 mins.
Add the lemon zest and pink peppercorns. Correct the seasoning with salt and pepper. At the end of cooking, add the herbs and chives.
Salt the fillets of cod on the flesh side.
Heat the olive oil over high heat in a frying pan, and then fry the fish on the skin side for 3 to 4 mins. Finish cooking on the flesh side for 3 mins, sprinkling with lemon juice after cooking. Serve the cod on a bed of leeks.