Preheat the oven to 220C/425F/Gas 7.
For the filling, place all of the filling ingredients into a bowl and mix well.
For the turnovers, cut the puff pastry into four squares and brush with the beaten egg.
Place a tablespoon of the filling mixture onto each square, then fold on the diagonal to make a triangle shape. Pinch to seal the edges and brush with a little more beaten egg.
Sprinkle the turnovers with caster sugar and place onto a baking sheet. Transfer to the oven and bake for 10-12 minutes, or until puffed up and golden-brown.
For the raspberry sauce, place the raspberries, sugar, lemon juice and water into a mini food processor and blend until smooth.
To serve, place the turnovers onto plates with the raspberry sauce in a small bowl alongside and dust with icing sugar.