Pre-heat your oven to 180c and lightly grease a loose bottom cake tin with vegan butter.
Combine the milk and cider vinegar together and set aside. In a mixing bowl, cream together the vegan butter and sugar until pale and fluffy.
Whisk through the milk mixture then stir in the dry ingredients until smooth. Fold through your diced plums and trasnfer your cake batter into the cake tin.
Pop this into the oven for 40-45 minutes, until a skewer can be removed clean from the cake. Allow to cool a little, then remove the cake tin and leave to finish cooling on a wire wrack.
For the frosting, beat the butter to a pale and fluffy consistency, then gradually add in the sugar and cacao. Once smooth, lather over the cake and layer on your sliced plums.
