Pour the milk into a pan then add the butter, place over a medium heat until the butter dissolves into the milk. Allow to cool slightly.
Place all other ingredients into a bowl (apart from the plums), add the warm (not hot) melted milk/butter mixture and mix by hand until smooth.
Cover the bowl with a towel and allow the dough to double in size (this should take about 15-30 minutes).
Dust a working area with flour, knead dough again. Roll out onto the baking pan/tray.
Cover the dough with plum quarters and allow the dough to rise for about half hour - 1 hour. Then bake at 180C on a greased baking pan/tray for about 30 minutes or until golden brown. Remove from oven, allow to cool, then sprinkle with caster sugar.