Mix icing sugar and starch. Stir with 150 ml almond milk until smooth. Boil up the rest of the milk in a pot. Stir the starch mixture into the boiling milk, bring to the boil and simmer for at least 1 minute.
Remove the pudding from the heat and season to taste with rose water. Pour immediately into four bowls or cups, cover directly on the surface with cling film and allow to cool. Coarsely chop the pistachio seeds and crumble the rose petals. Serve almond pudding sprinkled with pistachios and petals.