For the beer-braised beef cheeks, place the beef cheeks into a large bowl then add the garlic, bay leaf and thyme sprigs and pour over the ale to cover. Leave in the fridge to marinate for at least 6 hours, or overnight.
Once marinated, preheat the oven to 150C/130C Fan/Gas 2.
Lift the beef cheeks from the marinade and cut each of them in half. (Reserve the marinade.)
Heat the vegetable oil in an flameproof casserole over a medium to high heat. Add the marinated beef cheeks and fry for a few minutes on each side until browned on both sides. Pour the reserved marinade into the casserole, add the beef stock and bring the mixture to a gentle simmer.
Cover the casserole with aluminium foil, then braise in the oven for 6 hours, or until the beef cheeks are very tender and the volume of liquid has reduced and thickened. Alternatively, cook the beef cheeks in the slow cooker (set to a low heat) for 12 hours or overnight.
When the beef cheeks are cooked, remove them from the sauce using a slotted spoon and set aside. Bring the sauce to the boil, then reduce the heat until the sauce is simmering. Simmer the sauce until it has thickened enough to coat the back of a spoon. Season, to taste, with salt and freshly ground black pepper.
For the garnish, bring the onions and ale to the boil in a small saucepan. Reduce the heat until the mixture is simmering, then simmer gently for 45 minutes, or until the onions are tender all the way through. Set the pan aside to allow the contents to cool.
Prepare acidulated water by filling a bowl with cold water and adding the lemon halves to it.
Peel the salsify and cut into 5cm/2in batons. Add each baton to the acidulated water straight away to stop it from browning.
Bring a saucepan of water to the boil. Drain the salsify and lemons, add the salsify to the boiling water, then squeeze the juice from one of the lemon halves into the water. Reduce the heat until the water is simmering and simmer the salsify for 8-10 minutes, or until just tender – check how tender it is by piercing it with the tip of a knife. Drain well and set aside.
For the pearl barley risotto, place the garlic and pearl barley into a heavy-based saucepan and just cover it with chicken stock. Bring the mixture to a simmer for 10-12 minutes, or until the pearl barley is tender.
Blend the parsley and 125ml/4½fl oz of the remaining chicken stock to a very fine purée in a food processor – this will take a good while.
Pour the parsley purée into the pan containing the cooked pearl barley, then stir in the cream and Parmesan until heated through. Season, to taste, with salt and freshly ground black pepper, then cover the pan and remove from the heat (this will prevent the parsley from losing its colour).
For the garnish, heat the butter in a frying pan over a high heat until foaming. Add the halved onions and fry for 3-4 minutes, or until just golden-brown. Add the blanched salsify and fry for a further 3-4 minutes, or until golden-brown.
Just before serving, return the beef cheeks to the sauce and warm through.
To serve, spoon some of the pearl barley risotto into the centre of each plate. Place one piece of beef cheek on top of each portion. Add a pinch of beef stock cube to each beef cheek. Separate out the petals of the onions and arrange them around the edge of each plate. Serve the salsify alongside.