Four-hour rolled shoulder of lamb with potato & celeriac smash & steamed veggies

INGREDIENTS

• 2 quality shoulders of lamb, boned, rolled and tied by the butcher
• sea salt
• freshly ground black pepper
• olive oil
• 1 bulb garlic, broken into cloves, unpeeled
• 4 red onions, peeled and quartered
• 1 small bunch fresh rosemary
• 2 tablespoons flour
• 1 litre organic chicken or lamb stock
• 400 g curly kale
• 400 g Savoy cabbage
• 400 g winter greens
• 400 g purple sprouting broccoli
• butter
• 1 large celeriac, peeled
• 1 kg floury potatoes, peeled and quartered
• 50 g butter
• 100 ml hot milk
• 1 good grating fresh nutmeg