After 30 minutes, turn the heat off. You need to be patient now, so let sit with the lid on for another 20-30 minutes (heat off) before serving - for the flavours to blend.
Carefully insert a spatula or a skimmer deep in the pot and take a spoonful or rice from the bottom and bring it to the surface. Do not stir, it's the combination of different colours that makes the biryani so particular: it has to be a mix of white, yellow and red rice.