For the plum pockets, remove the seeds from the plums and cut them into small pieces. Roll up the puff pastry and cut into squares. Mix milk and yolk and brush the edges with it.
Spread the plums in the center of each square. Mix the jam with rum or water and heat a little. Spread the jam on the plums and sprinkle with almond slivers.
Bake at 200 °C for about 15 minutes. Serve sprinkled with powdered sugar.