Preheat the oven to 220°C for conventional oven, 200°C fan assisted, 7 gas. Place the baking trays in the oven (without the baking paper).
Unroll the ready-rolled pastry cut in 8 equal rectangular, lightly score a 5mm border around the edge of each rectangle. Place 8 pieces of pastry on 2 separate baking paper sheets (unless you have a large oven/baking tray then you can fit all the pieces into 1 tray).
In a bowl beat the egg, water and a pinch of salt. Spread the egg wash around the border of each tart. Sprinkle each tart with almond ground, place the sliced plums and almond flakes over.
Bake for 15-20 minutes or until golden. Remove from the oven let it cool down on a cooling rack. Serve with a dust of icing sugar and ice cream.
For a crisp and golden bottom ensure the baking tray is hot before placing the tart and baking paper sheets in the oven (because no one likes soggy bottoms).
Adding the almond ground beneath the plums help to absorb the moisture from the fruits.