Clean and wash the celery and cut it into fine slices. Peel and chop onion and garlic. Heat the fat in a casserole. Fry celery, onion and garlic for about 5 minutes while turning.
Sprinkle with flour, sweat briefly. Add wine and cream while stirring. Bring to the boil and simmer for about 5 minutes while stirring. Season with salt and pepper.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Wash fish, dab dry, cut into 6-8 pieces. Spread a thin layer of mustard and season with salt and pepper. Place on the celery vegetables and bake in a hot oven for 20-25 minutes.
In the meantime wash the grapes, dab dry and cut in half. Clean the salad, wash it, spin dry and cut into strips.
Mix the grapes and salad into the celery vegetables and bake for about 5 minutes. Season vegetables with salt, pepper and 1 pinch of sugar. Baguette tastes good with it.