3 medium leeks, trimmed
1 onion, chopped
a few sprigs fresh thyme
350ml/12fl oz good-quality chicken stock
2 tbsp plain flour
1 tsp vegetable oil
1 tbsp butter
100g/31/2oz cr猫me fra卯che, optional
6 skinless, boneless chicken thighs (about 500g/1lb 2oz), cut into bite-sized pieces
100g/31/2oz good-quality ham, torn into bite-sized pieces