For the chicken, heat the oil in a pan over a medium heat and cook the chicken portions, turning frequently, for about 5-6 minutes, or until browned on all sides.
Meanwhile, bring the stock to the boil in a large saucepan. Stud one of the onion quarters with the two cloves and add to the pan along with the remaining onion quarters, the chicken, carrot, celery, bay leaves, thyme, paprika and garlic. Simmer very gently, uncovered, for 30-45 minutes, or until the chicken just starts to fall apart. Remove the chicken from the pan and place into a roasting tin. Strain the stock through a sieve into a bowl.
Preheat the oven to 180C/350F/Gas 4.
For the sauce, return the strained stock to the pan, bring to the boil and simmer until the liquid has reduced by half.
In a bowl, for the sauce, mash the flour and butter together to make a paste (this, in chef terms, is a beurre manié). Whisk this paste into the stock along with the brandy and simmer for 3-4 minutes, until thickened and smooth. Add the chorizo and season, to taste, with salt and freshly ground black pepper.
Pour this sauce over the chicken in the roasting tin and sprinkle over the grated cheese. Transfer to the oven and bake for 10-15 minutes, or until the cheese is bubbling and lightly browned.
To serve, place portions of the chicken onto four serving plates and serve with the jacket potatoes and green beans.