Place the butter and harissa sauce in a bowl and use a fork to blend until well combined into a paste.
Turn on the oven to 250° C, air circulation, rack at the middle.
Use a large oven proof roasting pan and place in it the potatoes along with the carrots, onions and garlic. Pour the beer, drizzle with the oil, season with salt and pepper and sprinkle all-over the coriander and the thyme. Cover with foil and place in the oven for 45’.
In the meantime, remove the chicken from the fridge at least 1 hour before cooking. Add ⅓ of the harissa butter inside the cavity of the bird and rub with your fingers. Liberally season with salt and pepper the inside of the bird.
Carefully lift the skin of the bird and rub another ⅓ of the harissa butter all over the breasts and towards the thighs. Gently massaging and pressing the skin rub the remaining of the harissa butter all-over the chicken. Tag the legs to the inside of the thighs and tie tightly the thighs together and then around the chicken. Season with some more salt and pepper.
Back to the dish with the potatoes, remove from the oven, uncover and place a high rack on top of the potatoes. Add on the rack the chicken, breasts side up.
Reduce the oven’s temperature to 180° C and cook for 90’ to crisp and colour the skin. Halfway flip the bird to c-colour the other side of the chicken for about 25’. Then flip back and cook for the remaining 20’. If you an instant-read thermometer, then insert it into the thickest part of the breasts aiming for 80° C.
Take off the oven, cut the chicken and serve with potatoes, onions and carrots.