Roll out the pastry on a lightly floured surface a little larger than a 23 cm (9 inch) fluted flan tin. Lift the pastry over a rollng pin, drape into the tin and press over the base and sides. Trim off any excess pastry, and prick the base with a fork. Chill for 30 minutes.
Line the tart with nonstick baking paper, add baking beans and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15 minutes. Remove the paper and beans and bake for a further 12–15 minutes until the pastry is crisp and golden. Leave to cool.
Put the sugar, lime juice and kaffir lime leaves or lime rind in a saucepan and heat gently to dissolve the sugar. Bring to the boil and simmer for 5 minutes. Leave to cool for 5 minutes, then strain into a clean pan.
Stir in the eggs, egg yolks and half the butter and heat gently, stirring, for 1 minute or until the sauce coats the back of the spoon. Add the remaining butter and whisk constantly until the mixture thickens.
Transfer the lime mixture to the pastry case and bake for 6–8 minutes until set. Leave to cool and serve warm dusted with icing sugar.