Whizz garlic, celery and carrot in a food processor until finely chopped but not mushy. Zest the lemons and squeeze the juice of one half. Crush the peppercorns and juniper berries together in a pestle and mortar.
Heat the olive oil in a large, deep saute pan. Mix the flour and salt in a bowl and coat the chicken. Brown it over a high heat for 2-3 mins each side. Remove from the pan. Add the vegetables, herbs and spices. Cook gently for 5 mins.
Return the chicken to the pan, pour in the wine and bubble for 2 mins. Add the stock and lemon juice and half the zest. Bring to the boil, cover and simmer for 20 mins until the meat is cooked through. Sprinkle over parsley and rest of zest.