Preheat the oven to 190°C.
Slit the chicken skin and insert three truffle slices under the skin of each breast.
Season both sides of the chicken with salt and pepper.
Finely slice the remaining truffle and set aside.
Sear the chicken skin-side down in a medium-hot ovenproof pan for 3 minutes until golden.
Turn the chicken and roast in the oven for 20 minutes until cooked through.
Boil the leeks for one minute, then refresh in ice water and drain.
Repeat the boiling and refreshing process for the potatoes and then the pancetta.
Remove the chicken from the oven and rest under foil for 5 minutes.
Fry the potatoes and pancetta in olive oil for 2 minutes until golden.
Add the leeks, chervil, and most of the sliced truffles to the pan.
Deglaze the frying pan with water, then stir in butter and the remaining truffle slices.
Plate the vegetables and pancetta, reserving the pan liquid.
Carve the chicken into three pieces and serve over the vegetables with the sauce.