Peel 1 small celeriac (celery root) and 1 whole Granny Smith apple and slice into wedges.
Supreme chicken and remove skin and bone, reserve chicken thighs for another use or use skinless, boneless chicken breast.
Peel and slice garlic and shallots and add to peeled celery root and apple.
Add 1 cup chicken stock and 1 cup cider to a deep sided skillet and add the chicken breasts.
Add 2 cloves thinly sliced garlic, 2 whole thinly sliced shallots, 3 sprigs fresh thyme, and 1 small celeriac and 1 whole Granny Smith apple, peeled and quartered.
Bring to a boil, then reduce heat to medium and poach the chicken and vegetables for 20 minutes or until the chicken is cooked. The poaching broth should be at a light simmer and not boiling.
Remove the chicken to a platter.
Add 1/2 cup crème frîache to the broth and vegetables, remove the thyme sprigs and stir to combine.
Return the chicken and apple and celeriac to the broth and serve with fluffy mashed potatoes.