For the tart, blend the flour, icing sugar and butter in a food processor until the mixture resembles breadcrumbs.
Add the egg yolk, orange zest and mint and blend again, adding cold watera tablespoon at a time, until the pastry just comes together.
Roll out the dough out onto a clean, lightly floured work surface until it is the size of the base of a small frying pan. Heat the pan over a medium heat and fry the pastry for 2-3 minutes on both sides, or until pale golden-brown.
Arrange the plum slices on top of the pastry circle. Scatter the butter pieces and caster sugar over the plum slices and continue to fry for 3-4 minutes until the heat melts the butter and the sugar is gooey.
For the vanilla cream, mix the cream with the icing sugar and vanilla seeds.
To serve, turn the sweet plum tart out onto a serving plate, and place a spoonful of the vanilla cream next to it.