Preheat oven to 180°C (350°F). Place the pineapple, water and ½ cup (110g) sugar in a wide saucepan over medium heat. Bring to the boil and cook for 15 minutes. Remove the pineapple and set aside.
Upside down cakes are really easy to make, but usually the reserve for pineapples (and if you’re going that route, I do recommend Marcus Wareing's Pineapple Upside-Down Cake). Plums offer a nice twist ...