Halve the oranges and scoop out the flesh. Push the flesh against a sieve or through a muslim cloth to extract the juice. Place the empty orange cups in the freezer.

In a medium saucepan, stir the orange juice, castor sugar and water together. Bring to the boil, and then reduce the heat and simmer for 5 minutes. Remove from the heat and allow to cool.

In a food processor, blend the frozen fruit and syrup together until smooth. Freeze for 3–4 hours, or until set. Scoop the sorbet into the frozen orange cups and decorate with poppy seeds.