Finely chop the shallots and carrots and fry in the oil or lard. Add the tomato paste and mustard. Then dice the fresh tomatoes and add them. Braise everything for 5 minutes, deglaze with prosecco, simmer and then pour in the broth. Simmer a little, then add the fish fillets cut into strips. Bring again to just before the boiling point, stir in the creme fraiche and only let the fish simmer for about 10 minutes.