Rinse the chicken in cold water (inside and out), pat dry. Mix the lemon zest with all the other ingredients up to and including the pepper. Use the mixture to season the chicken, inside and out. Place the sprig of thyme inside the chicken. Brush the chicken all over with the clarified butter and transfer to the casserole dish, breast side down. Prick the garlic cloves several times, place next to the chicken along with the potatoes.
Roast for approx. 15 mins. in the lower half of an oven preheated to 240°C. Turn the oven down to 220°C. Remove the casserole dish. Turn the chicken, drizzle the wine over the potatoes, salt the potatoes. Slice the reserved lemon and arrange between the potatoes. Continue roasting the chicken with the potatoes for approx. 40 mins.
Plate up the salad and arrange the eggs and onion on top. To make the dressing, combine the lemon juice with the remaining ingredients and mix well, drizzle over the salad.