Joint the whole chicken into eight pieces consisting of thighs, drumsticks, and halved breasts.
Place the thighs and drumsticks into a large deep pan.
Add onion, garlic, thyme, and stock cube, then cover with approximately 1 litre of cold water.
Bring to a simmer over medium heat and cook covered for 9 minutes.
Add chicken breasts and simmer for another 5 minutes until fully cooked.
Remove chicken to a plate and cover with foil to keep warm.
Boil the cooking liquid uncovered until the volume reduces by half.
Clean and chop the mixed mushrooms and finely chop the fresh herbs.
Add double cream to the reduced liquor and simmer for 6 minutes to thicken.
Remove the garlic and onion from the sauce using a slotted spoon.
Return the chicken and its juices to the sauce to heat through.
Fry the mushrooms in vegetable oil and butter until golden brown.
Stir the chopped herbs into the sauce and adjust the seasoning.
Serve chicken topped with mushrooms and an optional drizzle of truffle oil.