Soak the gelatine in cold water until soft.
Lay two sheets of cling film on a clean surface and sprinkle the centre with half of the chopped herbs.
Press one trout fillet over the herbs. Place the gelatine leaves on top of the fish evenly. Place the second fillet on top, in the reverse direction (head to tail). Cover with the remaining herbs, press down firmly and roll the ballottine, starting from the tail, using the cling film to wrap it tightly. Twist the ends to make a sausage shape. Cover tightly with foil and refrigerate overnight.
Bring a large saucepan of water to the boil and weigh the ballottine. Add the ballottine to the water, still in its foil, for 3 minutes per 450g/1lb. Turn the heat off and leave in the water for 1 hour. Remove from the water and allow too cool. Put in the fridge overnight.
To make the beure blanc, place the wine, vinegar and chopped shallot into a small saucepan over a medium heat and reduce the liquid down by three quarters. Slowly add the butter, seasoning and lemon juice. Set aside.
Blanch the crayfish for 3–5 minutes or until they are cooked through and have turned bright red.
Meanwhile, blanch the shredded dark green cabbage for 1 minute and refresh under cold running water.
In a frying pan over a medium heat, sauté the crayfish with the girolles in a knob of butter. Add the shredded cabbage for 1–2 minutes.
Place the cabbage, crayfish and girolles between four plates. Slice the ballottine into four and place on top. Spoon around some of the butter sauce and serve.