Preheat oven to 220 degrees C
Season chicken with salt and place, skin side down, in a large pan
Drizzle the potatoes with the olive oil and arrange around chicken
Heat the pan over a medium heat and cook, without moving chicken but turning potatoes occasionally, until chicken skin is browned and crisp, for 15 minutes
Transfer chicken skin side up and potatoes to a plate, leaving as much fat in the pan as possible
Add the leeks and cook for a few minutes
Reduce the heat a bit add the harissa and garlic and cook for another few minutes
Add the fennel and lemon juice and cook for 5 minutes, stirring to make sure the fennel is covered with the sauce
Place the potatoes in a roasting tray and spoon the harissa and fennel mix over it
Place the chicken skin side up amongst the potatoes and fennel and roast for 15 - 20 minutes until the chicken and potatoes are cooked through and juices run clear when pierced
Transfer to a serving platter and top with a few fennel fronds