Cook the rice following pack instructions – don’t be tempted to cook it until al dente – it will not continue to cook in the milk later, so it needs to be nice and soft at this point.
Meanwhile, mix the cornflour to a paste with a little of the milk until smooth. Add this to a saucepan with the remaining milk, condensed milk, cinnamon, cardamom, nutmeg, vanilla and a good pinch of salt. Stir until smooth, then bring to a simmer. Turn down to very low heat and leave to gently infuse while the rice cooks.
When the rice is cooked, drain well, then add to the warm milk mixture. Turn up the heat and bubble until thick and creamy – this will take about 20-25 mins.
To make the blackberry compote, empty the blackberries into a saucepan, add the agave syrup and bring to a simmer. Boil for a few mins. Cool for a few mins before serving, or serve at room temperature with the rice pudding.