Heat half the fat, and in it first gently fry the cashew nuts until golden brown, and then put them to one side.
Fry the onion in the fat until wilted and golden brown, then add most of the curry paste and the potatoes, and cook for a few minutes more. Put to one side.
In a saucepan melt or heat the remaining fat, stir in the flour, and then gradually add the milk and cook until you have a smooth thick white sauce. Remove from the heat, and stir in the egg yolks and curried potato and onion.
Whisk the egg whites until firm, and fold them into the yolk mixture. Spoon into a lined, greased Swiss roll tray, and bake in a preheated oven at 200°C/400°F/gas mark 6 for 12 to 15 minutes, until the mixture is golden brown and just firm to the touch. Turn it out onto a clean tea towel, and carefully roll it up from one of the thin ends.
To make the filling, lightly crush the cashew nuts, and stir into the yoghurt with the herbs. Unroll the roulade, spread on the filling, and re-roll it.
Make the sauce by cooking the remaining curry paste with the juice, chutney and crushed cardamom seeds. Stir in the mango, and serve with the sliced roulade.
© 2000 Frances Bissell. All rights reserved.