Preheat the oven to 200C/400F/Gas 6. Slice the top off of the garlic bulb, rub with a small knob of the butter and wrap in aluminium foil. Place the garlic to roast in the oven for 30 minutes, or until softened.
Squeeze the garlic out of the bulb into a bowl and mash well to a purée. Set aside.
Season the lamb with salt and freshly ground black pepper. Heat an ovenproof pan until hot, add the lamb skin-side down and cook for 1-2 minutes.
Turn the lamb over and fry on the other side for 30 seconds. Then place the meat, bone-side down, into the pan. Place in the oven to roast for 12-18 minutes, or until cooked to your liking.
Remove the lamb from the oven and leave it to rest in a warm place for five minutes. Place the pan back on the heat, add the red wine, stirring well to release all the meat sediment from the base of the pan. Simmer for 1-2 minutes until the volume of liquid has reduced by half.
Add the chicken stock to the pan, bring to the boil then cook for a further 2-3 minutes until just thickened and reduced slightly. Season with salt and freshly ground black pepper.
Meanwhile, place the potatoes into a pan of salted water, bring to the boil and simmer for 15 minutes, or until tender.
Drain the potatoes and return them to the pan over the heat, to drive off any excess moisture. Mash the potatoes with a potato masher or ricer and add the smoked garlic, remaining butter and cream and beat to a smooth purée. Season with salt and freshly ground black pepper, to taste.
To serve, place a pile of mash into the centre of each plate. Carve the lamb racks into individual chops and place over the mash. Finish with a drizzle of the red wine sauce.