Use an oven-to-table fireproof dish which will allow the pigeons to fit side by side. A cast-iron one is perfect as it can be started on top of the stove, then put into the oven. Peel the onions, cut the bacon into thin strips and wipe the mushrooms. Heat the butter and lightly fry the bacon. Put on a warmed dish, and reserve; cook onions until lightly golden, sprinkling with sugar. Remove to dish. Cook the mushrooms in the same fat, and remove to the dish. Brown the pigeons in the fat, very slowly and carefully, and lift out. Work the flour into the fat, cooking until brown. Gradually add stock and wine, bring to the boil and strain. Rinse out the pan, put back the sauce and bring to the boil. Add all the ingredients, cover with greased paper and well-fitting lid. Cook at 300°F, 150°C, gas mark 2 for 2½-3 hours. Remove bunch of herbs before serving.