Preheat the oven to 180°C/350°F/Gas 4. Have six 200ml (7 fl oz) ovenproof ramekins ready (ceramic soufflé dishes are ideal). Prepare a bain-marie by half filling a roasting dish with hot water and place it on a sheet in the top third of the oven. Bring the milk, spices and golden syrup to the boil, cover with a lid and put aside in a warm place for 10 minutes. Beat the eggs, vanilla and demerara sugar for 30 seconds and gently whisk the hot milk mixture into them. Oil the ramekins and divide the cashew nuts between them, then pour the custard over the nuts. Place in the bain-marie and bake for 40 minutes.
Test the vattalapam by inserting a wooden skewer; it should come out clean, if a little moist. Let them cool in the ramekins before placing in the fridge for at least 2 hours to set (they will keep for up to four days). Run a knife around the sides and shake gently to remove the dessert. Serve with wedges of fresh tropical fruits.