Pick a wide, medium-deep pan that holds a lid. Slice the onion and sauté it in olive oil until translucent (about 15 minutes). Add the garlic at the end and fry it for 2-3 minutes.
Make the paste by finely chopping the sun-dried tomatoes, anchovies and capers. This is a Dalmatian version of the umami flavour. Mix the paste into the onions.
Layer the potatoes on top of the onions and the paste. Pour in water and wine. Season with salt (careful because the anchovies are salty!), pepper, bay leaves and rosemary. Put the lid on and simmer on medium-low heat until the potatoes are half done (about 15-20 minutes).
Prepare the fish by descaling and gutting it. Cut larger fish into fist-sized pieces and leave the heads on. Arrange them on top of the potatoes. The contents should be only 3/4 covered with liquid.
Cover the pot with the lid. Do not stir. Just shake the entire pan occasionally. Cook for about 10-12 minutes. Lastly, add the washed prawns or langoustines and cook for 3-5 more minutes. Prawns and langoustines are done when their tails turn opaque.
Sprinkle with chopped parsley and drizzle with more olive oil. Serve immediately.