Rinse the salted cod fillet under cold water to remove excess salt. Pat dry thoroughly with paper towels.

Boil the potato chunks/wedges in lightly salted water until just tender, about 10-15 minutes depending on size. Drain well.

While potatoes boil, heat the oil in a large frying pan over medium-high heat. If using flour, lightly dust the dried cod fillets.

Carefully add the cod fillets to the hot pan and fry for 4-6 minutes per side until golden brown and cooked through, easily flaking with a fork. Remove from pan and set aside.

Add the sliced onion to the same pan (add a little more oil if needed) and sauté over medium heat until softened and lightly browned, about 5-7 minutes.

Increase heat to medium-high, add the drained potatoes to the pan with the onions, and fry until crispy and golden brown on all sides, about 8-10 minutes. Season with pepper and check saltiness (remember the cod is salty!).

Serve the fried potatoes and onions alongside the cooked cod fillet. Top the potatoes with a dollop of sour cream.

Garnish with fresh herbs and serve with lemon wedges if using the optional ingredients.