1. Preheat oven to 180°C.
2. Grease and line with baking paper a deep 20cm round cake pan.
3. Melt 2 tablespoons of butter and pour into the base of the cake pan then sprinkle base with brown sugar.
4. Drain plums on kitchen paper and cut in half, remove stones and discard.
5. Place plums into the pan with the flat side down to cover cake pan base.
6. Sift flour and baking powder into a bowl and add the sugar. Melt the remaining butter, cool slightly.
7. Combine buttermilk, eggs, orange rind and vanilla essence. Make a well in the middle of the cake and begin to add the liquid folding and stirring with a metal spoon. Add the butter and stir.
8. Spoon the mixture into the cake pan and over the plums.
9. Cook cake on the middle shelf of the oven for 50-60 minutes or until golden and when tested by inserting a skewer into the cake the skewer comes out clean.
10. Stand cake in pan for 10 minutes before turning out onto a wire rack to cool
    

Shield cake with a piece of foil placed lightly over the top if the cake is browning quickly and not yet cooked.