Heat about two thirds of the butter and oil in a heavy based pan that can be put into the oven. Pre heat the oven to 160c
Soften the onions for 5 to 10 minutes. Then add the garlic, carrot and celery and cook for 2-3 minutes.
Remove the softened vegetables from the pan and set to one side
Raise the heat and brown the meat in batches
Return the vegetables to the pan and add in the wine and bouquet garni
Bring the mixture to a gentle simmer, put the lid on and place in the oven.
Cook for 3-4 hours, checking very occasionally stirring and adding a little water if necessary.
Half an hour before you want to eat, heat a little more butter and oil in a frying pan. Brown the shallots, then the button mushrooms, before adding both to the casserole and continuing to cook in the oven.
To serve, check and season with salt and pepper to taste and remove the bouquet garni