For the sauce, measure 450ml of just-boiled water. Mix the sugar and cornflour together, then add the boiled water, golden syrup and vanilla extract, and quickly mix. Pour it over the sponge then scatter over the coconut flakes. Put the dish on the middle shelf of the oven and bake for 35-40 minutes or until the top is crisp and feels firm – it should be floating on a bubbling caramel sauce. Leave to stand for 10 minutes, so the molten sauce settles, then serve spoonfuls with cold cream, if you like.