Pat the conger eel steaks dry with kitchen paper, then season generously with salt and freshly ground black pepper. Set aside.
Heat the extra-virgin olive oil in a large, shallow pan or casserole over medium heat. Add the chopped onion and cook for 8–10 minutes, stirring occasionally, until softened and translucent.
Add the sliced garlic and cook for 1–2 minutes, taking care it doesn’t brown.
If using plain flour, sprinkle it over the onion and garlic and cook for 1 minute, stirring, to remove the raw flour flavour.
Pour in the white wine, increase the heat and let it bubble for 2–3 minutes to cook off the alcohol, stirring and scraping the base of the pan.
Stir in the chopped tomatoes and saffron strands, then reduce the heat to medium–low and cook for 5 minutes.
Add the fish stock, bring to a simmer, then reduce the heat and simmer gently for 10 minutes. Season with salt and pepper to taste.
Gently add the conger eel to the sauce, turning to coat. Cook for 8–12 minutes over medium–low heat, or until the fish is opaque and flakes easily.
Remove from the heat, scatter over the chopped parsley and leave to rest for 2 minutes before serving.