Boil the washed potatoes with their skin on. Remove potatoes from the heat after 15-20 minutes or when ready (for this salad, the potatoes should be almost fully cooked through but still very slightly undercooked in the centre). Cool. Then, peel and cut into small dice.
Lightly salt and sear the cod on all sides in a hot pan until you get a nice toasted brown crust on all sides, and just cooked through (approximately two minutes on each side). Then flake the cod and set aside.
Peel the oranges, remove the segments (without membranes) and reserve 16 segments whole and roughly chop the rest into chunky pieces.
Finely chop the onion.
Remove seeds from tomatoes and chop them as finely as possible.
In a bowl, combine the diced potatoes, flaked cod, chopped onion, chopped orange pieces and tomato. Dress the ingredients right in the bowl, with the chopped olives, olive oil, white wine vinegar, a tablespoon of Espelette pepper and 1 - 1 1/2 teaspoons of salt, or to taste. Fold together the ingredients to incorporate all the flavors well and chill for at least an hour.
To serve, place individual cylinder molds in the center of each plate. Lightly pack the cod salad into molds. Place four reserved, whole orange segments on top of each cod salad and tumble over about a dozen pomegranate seeds. Unmold the salads and serve chilled.