Heat oil in a large frying pan and cook chicken for 3-4 minutes until golden brown. Set aside in a bowl, and then melt butter in same pan. Fry onions for 2-3 minutes then add Biryani paste and rice. Stir to combine.
Return chicken to the pan and add chicken stock and water. Bring to the boil then simmer for 12-15 minutes until rice has absorbed all the water and onions are tender.
Serve chicken Biryani on basmati rice with a spoonful of Greek yoghurt.