In a bowl, combine the maize, rice and potato flour with the salt. Gradually beat in the milk, a little at a time until the mixture is smooth. Add the eggs and beat well. Melt a little butter in a hot frying pan, then ladle out 50ml of batter (18 cm in diameter). Cook each pancake over a medium heat for about 1 min. on each side, or until golden. Cook the rest of the pancakes, melting a little butter in the pan before each one. Give the batter a good whisking between each pancake, as the flour tends to sink to the bottom. Roll the pancakes up individually and sprinkle with icing sugar.
Cut the passion fruits in half and scoop out the pulp. Combine with the yogurt and serve with the pancakes.