Boil raspberry vinegar, fish stock, water in a pot, add salt and pepper to taste. Reduce the fire. Gently insert steaks into it and cook 5-7 minutes. Remove the steaks and add potato starch to the broth, and mix well to have a sauce. Cut pineapple into 20 slices and rub each carefully in rapeseed oil and place on a hot grill pan. Season to taste with salt and pepper. Prepare fries according to package instructions.
Place halibut steak on a plate and pour sauce over it. Serve fries and a slice of pineapple next to fish and sprinkle with chili.
Use peaches or nectarines, instead of pineapple.