Bring the red wine to the boil with the sprigs of thyme, parsley, bay leaves and peppercorns, then leave to cool for 1 hour; pour the wine over the chicken pieces and marinate for 12 hours.
Fry the bacon in a frying pan, remove with a slotted spoon; add the oil to the pan and fry the onions until softened; remove to casserole dish.
Remove the chicken pieces from the marinade and pat dry with kitchen paper.
Dust the chicken pieces with a little flour, then put them in the frying pan and brown them lightly; pour in the warmed brandy and flambé it (or cook off alcohol); transfer the chicken pieces and liquid to the casserole and add the bacon, strained marinade (with tomato paste stirred in), garlic and mushrooms; cover and cook in a preheated oven at 300F for about 1 hour.
In the meantime, fry the small onions in butter with the sugar and a little water until glazed; add to the casserole and cook for a further 30 minutes; if the sauce needs thickening, stir in a few small knobs of beurre manié.
Remove the casserole from the oven and sprinkle the chopped parsley over before serving.