For the purée, soak the beans in water overnight then drain well. Place the beans in a pan of fresh water and bring to the boil. Add the bay leaves and rosemary sprig, cover with greaseproof paper and simmer until cooked.
Remove the bay leaves and rosemary and drain the beans over a large bowl to reserve the cooking liquid. Place the beans in a blender, season with a little salt and add the butter and cream. Blend until you have a silky smooth purée, adding a little of the cooking water if necessary, and set aside.
Peel and core the pears, cut into 1cm/½in cubes and cover with the lemon juice and a little water until needed. Reserve the pear skin.
Preheat the oven to 180C/350F/Gas 4. Season the beef cheeks with salt and fry in a little oil in a large ovenproof pan until browned on all sides. Remove the meat from the pan and set aside. Fry the onion and garlic in the same pan until brown then return the meat to the pan and deglaze with the port and orange juice. Lower the heat and reduce the liquid until it is syrupy then add the stock, pepper, orange zest and pear skin. Cover with greaseproof paper and place in the oven for about three hours or until the meat is very tender.
Cook the onions with a knob of butter and a little water. In another pan, fry the pear cubes in a knob of butter.
When the beef is cooked, remove from the pan. Place a sieve over a bowl and strain the cooing liquid. Pour the liquid into a clean pan and reduce to a syrupy consistency then whisk in the remaining butter and the chocolate.
To serve, dress the plate with a spoonful of the bean purée, the cooked pears and button onions. Lay a piece of beef cheek on each plate and spoon over the sauce.