1organic chicken (about 1.8kg)4golden shallots, halved4tarragon sprigs1bunch of baby leeks, trimmed, washed1head of garlic, cloves separated185 ml (¾ cup)chicken stock125 ml (½ cup)verjuiceTo serve:mashed potatoTarragon butter1head of garlic250 gmbutter, softened1cup (loosely packed) tarragon leaves2lemons, finely grated rind only (quarter and reserve lemons to stuff chicken)
For tarragon butter, preheat oven to 200C. Wrap garlic tightly in aluminium foil and roast until very soft (25-30 minutes). Squeeze garlic from skins, transfer to a food processor, add remaining ingredients, season generously and process until smooth. Set aside.
Rinse chicken inside and out under cold running water, then pat dry with absorbent paper. Season cavity and stuff with shallot, tarragon and reserved lemon.
Using your fingers, separate skin from breasts and legs, being careful not to break skin. Spoon two thirds of tarragon butter between skin and flesh, spreading thickly and evenly. Truss chicken legs and set aside.
Place leeks in the base of a flameproof roasting pan large enough to fit chicken snugly. Scatter over garlic and pour in stock and verjuice. Place chicken on top, season to taste, then roast, basting frequently with pan juices, until golden and juices run clear when thigh is pierced with a skewer (50-60 minutes). Transfer chicken and leeks to a plate, cover with foil and keep warm. Simmer pan juices over medium-high heat until reduced by half (10-12 minutes). Whisk in remaining tarragon butter a little at a time until emulsified and season to taste. Serve chicken with pan juices, and leeks and mash passed separately.