Preheat oven to 180 degree C.
Take butter, sugar and vanilla. Mix well.
Add cocoa powder, baking powder and salt and mix well.
Add in custard powder, flour and mix well. Mix to a form a dough.
Take a small portion, roll it into a ball. flatten it and place on a baking pan. Place a cashew on top
Bake for 12 to 15 mins. Remove and cool completely.