Combine flour, cinnamon, baking powder and sugar in a bowl. Make a well in the centre and mix in egg, milk and butter to a smooth batter.
Spoon into a buttered rectangular baking dish and arrange plum halves on top, cut side down. Pour over extra melted butter and sprinkle with 2 tablespoons extra sugar, extra cinnamon and mixed spice.
Bake at 200C for 25-35 minutes until golden brown.
Boil reserved syrup with remaining castor sugar for 10 minutes until reduced and syrupy. Serve squares of cake with plum syrup and cream.
» Metric Converter