Turn on the oven to preheat to 190 degrees. Place the potatoes in an ovenproof dish. In a skillet over medium heat, heat half of the butter, add the onion, and fry, stirring occasionally, for about 5-6 minutes. Transfer the fried onions to the potatoes and stir.
Peel the garlic cut 2-3 cloves into plates and place between the potato pieces. Also put thyme and bay leaf in the potatoes, salt, and pepper to taste.
Pour 450 g of broth over potatoes and place in a preheated oven. Cook, stirring once, for 50-60 minutes, until the potatoes are soft. Mix the remaining broth with the wine.
Put the fish fillet between potatoes, brush with wine sauce, cook for 10-15 minutes.
Chop the remaining garlic finely. Melt the remaining butter in a saucepan, add garlic, and stir. Pour 2/3 of the parsley and bread crumbs into a saucepan, add a little salt and pepper. Put this mixture on the fish fillet, lightly pressing down with a spoon.
Sprinkle the fish with olive oil and place in the oven again for 10-15 minutes. Serve with the remaining parsley.