Method

• 1.
  Preheat oven to 180°C/160°C fan-forced.
• 2.
  Combine mustard and butter in a bowl to make a smooth paste. Using your hand, gently loosen the skin from the flesh of the chicken breasts and thighs, being careful not to tear it. Spread butter as evenly as possible under the skin.
• 3.
  Place chicken, breast-side up, in a flameproof roasting pan and tie legs with kitchen string. Roast, turning pan around once to evenly brown chicken, for 1 hour, or until evenly cooked (the colour might be patchy because of the caramelisation of the butter).
• 4.
  Remove chicken from the oven and turn chicken breast-side down to rest for 15 minutes in the pan (the resting juices will rush into the breast meat). Transfer chicken, breast-side up, to a plate and cover with foil to keep warm. Reserve pan.
• 5.
  Place the pan with the resting juices over low heat and add the fennel seeds. Stir for 1 minute, or until fragrant, then add the spinach and garlic and bring to a simmer, stirring to wilt the spinach lightly. Stir through tarragon and season to taste.
• 6.
  Carve the chicken and serve with the buttery spinach and sauce.