Preheat the oven to 180°C (350°F) and line a 22cm round spring-form pan with baking paper and grease the sides thoroughly.
Drain the tin of plums and then spread them in an even layer on paper towels, remove any stones and pat with a few paper towels to remove as much liquid as possible and set aside.
In a food processor or stand mixer mix together the softened butter, caster sugar, egg, vanilla extract and lemon rind. Mix until well combined and smooth.
Add in the flour and baking powder and pulse in and them mix together completely.
Press two thirds of the dough into the base of the prepared pan.
Arrange the plum halves over the base in an even layer.
Dot the remaining dough on top of the plums in an even layer and place in the oven for around 40 minutes or until the top and and sides are golden brown.