Tip the flour, salt and sugar into a large bowl. Cube thebutter and rub it into the dry ingredients with your fingertips until no large lumps remain.
Stir the yoghurt in with a knife and bring the mixture together into a ball with your hands.
Roll out the pastry on a floured surface to line a 23cm greased loose bottom tart tin. Leave in the fridge or a cool place to rest whilst you get on with the filling.
Using the same bowl, cream the butter with the sugar until light and fluffy.
Beat in the eggs.
Stir in the almonds, followed by the flour. Finally add the amaretto or almond extract and stir until just combined.
Stone the plums and cut into halves.
Spoon the filling into the pastry case and push the plums slightly into the filling.
Sprinkle the reserved 1 tbsp of sugar over the plums.
Bake on the middle shelf in a preheated oven at 180℃ (350℉, Gas 4) for 30-35 minutes or until the tart is risen, golden and set. If the pastry looks as though it might be burning, place a piece of foil loosely over the top for the last five minutes or so.
Leave to cool before removing from the tart case.
Please note: calories and other nutritional information are per serving. They're approximate and will depend on exact ingredients used.