Marinate ahead: overnight in the fridge is noticeably better than an hour, and the yoghurt does the tenderising.
Brown in batches: a crowded pan steams the chicken instead of colouring it, and that colour is most of the flavour in the finished sauce.
Blend before the chicken goes back: the sauce is meant to be smooth, and blending it with the chicken in shreds the meat.
Mango chutney: brands vary a lot in sweetness. Add half, taste, then decide.