Preheat the oven to 190°C (gas mark 3). Grease six 150 ml soufflé dishes with butter. Cream the butter and sugar in a bowl with a whisk. Fold in lime zest and juice and passion fruit pulp.
Add the egg yolks one at a time, whisking each in thoroughly. Mix the flour with the baking powder and fold in alternately with the milk until everything is blended.
In a second bowl, beat the egg whites until stiff. Gently fold a quarter of the beaten egg whites into the batter with a pastry scraper to loosen it up. Then fold in the remaining beaten egg whites. Pour the mixture into the prepared ramekins.
Place them in a roaster and pour in hot water up to half the height of the ramekins. Bake the puddings for 20 – 25 minutes until they are firm.