Cut the chicken breast into pieces. Place in a food processor with the egg white, salt, and pepper. Process until smooth, then add the cream. Process for another minute, then add the Saint Agur cheese in pieces
Place the boned guinea fowl skin-side down on a large sheet of cling film. Season with salt and pepper, then spread the stuffing in the center
Gently roll up the guinea fowl and wrap it tightly in cling film. Add two more layers of cling film and tie the ends
Submerge the ballotine for 30 minutes in a large pan of simmering water. Remove the ballotine and let it cool. In the meantime, Preheat the oven to 180°C
Remove the film from the ballotine and place it in an ovenproof dish. Drizzle gently with olive oil and roast in the oven for 35 to 40 minutes
Pour the chicken stock into the dish 10 minutes before the end of cooking
Cook the cleaned and chopped mushrooms for 10 minutes in a buttered pan over medium heat. Add the chestnuts. Grind some pepper over everything and cook for another 5 minutes
