This garnish is sprinkled on the top layer of the biryani before it is served. It adds a wonderful rich depth of flavour and it’s what makes the biryani so ridiculously delicious. There is an alarming amount of butter, but trust me, it works! The onions are basically shallow-fried in the butter, which is infused with lemongrass, curry leaves, cinnamon and spices. It’s decadent but frighteningly good.