Heat the oven to 200°C.
Sprinkle the chicken with salt and pepper. Place half a lemon, the garlic and lemon thyme inside. Transfer the chicken into a roasting pan then spread the butter all over its skin.
Put in the oven, 20 minutes per 500g plus 20 minutes, while basting occasionally. The chicken is cooked through when juices run clear after you poke the thickest part of the thigh with a fork or a skewer. Take out of the oven and set aside.
Add a little water and a dash of lemon into the roasting tray then deglaze.
Making the caramelized chicory: when the chicken is in the oven, heat half of the butter and the salt in an ovenproof pan. Sweat the onions but don’t let them brown.
Stir in the water, sugar, chicken stock and bouquet garni. Toss in the chicory then bring to the boil.
Turn off the heat and cover with foil. Roast along with the chicken until the chicory becomes tender. This should take about 30 minutes.
Take out of the oven then place the chicory on a rack. Allow to cool down then halve the chicory. Put the rest of the butter into a frying pan and set over medium heat. Place the chicory into the pan and caramelise.
Serve the roast chicken with the chicory and pour over the chicken cooking juices.