Pre-heat oven to fan assisted 160C / 180C / gas 4
Lightly oil a lined rectangular tray measuring about 30cm x 20cm.
Cream the butter and sugar together with an electric whisk (or a wooden spoon) until light and fluffy before gradually beating in the eggs.
Sieve the flour and baking powder in to the mixture and fold in along with the almonds and orange zest.
Mix in the orange juice until combined - it should be of a dropping consistency. If necessary add in a couple more tbsp of orange juice.
Pour the cake mixture into the prepared tray and level with a spatula.
Gently press the plums into the cake mixture and top with the flaked almonds.
Bake for 35-40 mins or until a skewer comes out clean when inserted into the cake.
Allow to cool in the tray before slicing the cake.