Boil 1 litre of water with brine ingredients until salt dissolves, then cool.
Submerge chicken in brine and refrigerate for at least eight hours.
Preheat oven to 220°C and place chicken over chopped vegetables, garlic, and thyme in a tray.
Roast chicken for 40-50 minutes until juices run clear when pierced.
Boil potatoes in salted water for 12-15 minutes until tender and drain.
Rice potatoes, then beat with butter and cream until smooth and season.
Reduce white wine by half in a pan, add stock and tarragon, and reduce again.
Cook morels in the sauce for two minutes, then stir in tomatoes and chives.
Serve chicken pieces with mash and pour the chasseur sauce over both.