Put the onion, ginger, garlic, chillies
and coriander stalks in a small food
processor, or pestle and mortar, and mix
to a paste. Meanwhile, heat the butter or
ghee and oil in a large pan. Add the paste
to the pan and stir-fry for 5 mins to
soften. Add the garam masala and cook
for a further 2 mins until aromatic.
Meanwhile, toast the cashew nuts in
a small pan until golden. Tip half into the
food processor and blend until finely
ground. Set aside the remaining cashews.
Add the blended cashews, the
tomatoes and the chicken stock to the
pan. Season and bring to a boil, then
lower the heat and simmer, covered
with a lid, for 45 mins. Add the prawns
and cook for a further 2-3 mins until
they turn pink, then add the yogurt
and double cream and stir well. Scatter
with the coriander leaves and the
remaining cashew nuts, and serve
with rice and naan bread.