Preheat the oven to 200°C.
Mix the butter with the garlic, thyme, salt and pepper and lemon zest.
Using sharp kitchen scissors, cut the chicken along the backbone. (You can remove the backbone, if preferred). Flatten the chicken by placing it skin-side up on a cutting board and pushing down the breastbone.
Cut the potatoes into rings, the fennel bulb and onion into slices. Lay these in a large, lightly oiled baking tin. Season with salt and pepper. Put a roasting rack on top and place the chicken on it.
Rub the chicken all over, then under the skin with the lemon butter. Crumble the remaining mixture over the potatoes and fennel.
Cut the lemon into rings and put them under the chicken and in the tray.
Put the tray in the oven and roast for 15-20 minutes, or until the chicken is golden.
Turn down the heat in the oven to 170°C.
Take the tray out and turn over the potatoes.
Pour over the lemon juice and wine.
Put the tray in the oven and bake for another 25 minutes.
If the chicken is cooked through (check it at the thighs), then remove it to a plate, cover and keep warm.
Meanwhile, turn up the heat in the oven and brown the potatoes (if you want them crispy) and add your greens if you like.
Carve the chicken and serve with the vegetables and jus.