Take the sole fillets and keep the trimmings. Prepare the stock:put the trimmings in a roundel with the onion, the bouquet garni and the white wine, let reduce almost to dryness and add 50 cl of water, salt and pepper, cook for 30 minutes uncovered at a low simmer . Then strain through a sieve strainer, pressing well on the ingredients.
Preheat the oven to th.6 (180°C).
Peel and chop the shallots. Put them in the bottom of a gratin dish, place the rolled fish fillets on top and hold them in place with wooden skewers. Add the stock, cover with a sheet of aluminum foil. and put in the oven for about ten minutes.
Drain the fillets and keep them warm in a serving dish. Pour the stock into a saucepan and reduce it over high heat. Add the cream and the mustard, whisk for 3 minutes, still on high heat.
Coat the fillets of sole with this sauce and serve immediately.
You can decorate the dish by garnishing it with triangles of bread toasted with butter and served with braised and lemony hearts of fennel.
