Put the tamarind paste, sugar and golden syrup in a small saucepan. Add the lime rind and juice and the measured water and bring to the boil, stirring until the sugar has dissolved. Simmer for 5 minutes.
Mix the cornflour with a little extra water in a cup, then add to the sauce with the butter, bring back to the boil and heat, stirring until thickened. Set aside to cool for 10 minutes.
Divide the mango and ice cream among 4 glass dishes, then drizzle a little of the sauce over the top and decorate with extra lime rind curls, if liked. Serve the remaining sauce in a small jug.