Cook rice mixture in boiling salted water according to package instructions. In the meantime, peel prawns, except for the tail fin, and remove the intestines. Wash shrimps and pat dry. Clean and wash the fennel and cut out the hard stalk.
Chop the fennel greens. Slice the fennel finely. Onions peel, very finely dice. Cut 150 g butter into small cubes, chill. Melt 1-2 tablespoons of butter in a pan. Fry 1 diced onion and fennel for about 10 minutes at medium heat.
Turn from time to time, season with salt and pepper. Fry the prawns in hot oil while turning for about 2 minutes. Add the remaining onion cubes and fry briefly. Season with salt and pepper. Deglaze with fish stock and Pernod, boil down almost completely for 2-3 minutes over high heat.
Remove the prawns and add vinegar. Stir in cold butter cubes bit by bit with a small whisk. The sauce must not get too hot. Arrange rice, fennel vegetables, prawns and sauce on plates.
Sprinkle with chopped fennel green and pepper from the mill.