preheat the oven to 150° Celsius

grease a spring form tin (if you look closely at the photo you will see I lined the tin, but it is not easy to get the paper off so next time I will not line the tin)

halve the vanilla pod lengthwise, remove the seeds and discard the pod (put the pod into your sugar container to make vanilla sugar)

beat the caster sugar, vanilla seeds and eggs until light and fluffy

add the lemon zest, milk and butter

stir in the ground almonds, flour and baking powder

pour half the mixture into the tart dish

arrange half the apple slices on top and dust with caster sugar

pour the remaining mixture over the apple slices

arrange the remaining slices on top and dust with caster sugar and cinnamon

bake for 55-60 minutes and then leave to cool