Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4
Grease a 9" pin tin, or flan dish, with the butter and sprinkle caster sugar all over it
Arrange the prepared plums in the tin in your desired pattern
In a bowl whisk the eggs, caster sugar, milk and vanilla extract together
In another bowl, measure out the flour. Slowly pour the egg mixture into the flour bit by bit, whisking with each addition, until a smooth batter is formed
Pour the batter over the plums, start in the centre and the batter will naurally fill up the gaps between the fruit
Bake for 30 minutes or until puffed up, golden brown and with a slight wobble
Serve warm with custard or ice cream. Or allow to cool to room temperature and serve with cream
Leftovers can be kept in the fridge for 2 days, but it is best eaten on the same day as otherwise it can go soggy