4 Portobello mushrooms, sliced听
8 garlic cloves, peeled but left whole
1 onion, thickly sliced
1 tbsp finely chopped fresh parsley
1 tbsp finely chopped fresh tarragon
3 anchovy fillets听
500ml/18 fl oz chicken stock听
20 prunes, stones removed
2 bay leaves听
salt and freshly ground black pepper
1 tsp fennel seeds
4 tbsp vegetable oil
splash white wine vinegar听
1 whole duck
4 good-quality bread buns
150ml/5fl oz white wine听