Firstly preheat the oven to 180°C, roll out the pastry and line the pastry in 4 individual tart cases. Then line with nonstick baking paper over the top and add some baking beans.
Bake for 15 minutes, then take out the beans and finish off until golden.
Then go on to make the curd. Place a saucepan of water on to boil, and in a bowl that fits snugly on top of the saucepan, add the grapefruit juice, lemon juice, zest, egg yolks, butter, sugar and salt, this cooking method is called en bain marie.
Place the bowl on top of the saucepan and heat while whisking until thickened. Then take off and pour into the tart cases.
Whisk the egg whites to soft peaks, and gradually add the sugar, one spoon at a time, whisking in-between, until stiff and glossy. Then spoon onto the tarts and top with a sprinkling of crushed pistachios.
Finally pop back in the oven for 15 minutes until a little golden and serve with the refreshing grapefruit segments on the side.