For the pastry
Sift the flour and salt into a mixing bowl.
Cut the butter into small cubes and add to the flour. Rub in the butter, at the same time lifting the flour well out of the bowl to incorporate as much air as possible.
When the mixture resembles dry breadcrumbs, add the sugar.
Then sprinkle over 3 tablespoons of cold water and, using a palette knife, bring the mixture together until it begins to form clumps. Add a little more water (no more than 1 tablespoon) if the mixture seems dry. Using your hands, bring together into a ball by kneading lightly. Cover in cling film/plastic wrap and refrigerate for 20 minutes to relax the pastry.
(Alternatively, use a food processor.)
Roll out the pastry on a lightly floured surface until it is 5cm (2 inches) larger than the size of the tart tin. Carefully transfer to the tin without stretching the pastry. Gently press down into the sides of the tin, then trim by running the rolling-pin over the top to cut the pastry level with the rim. Return to the fridge for a further 20 minutes to firm up.
Meanwhile, preheat the oven to 200°C (400°F) (gas mark 6).
Prick the pastry base all over, line with baking paper and add baking beans, making sure they spread to the edge. Bake for 15 minutes.
Remove the paper and beans and bake for a further 10–15 minutes until golden. Put to one side to cool a little before filling.
For the filling
Meanwhile, make the filling. Reduce the oven temperature to 150°C (300°F) (gas mark 2).
Strain the juice of the lemons and orange into a bowl.
Add the sugar, eggs, and egg yolks and whisk just enough to blend in the eggs. Whisk gently to avoid the mixture becoming too frothy.
Stir in the cream.
Then strain the mixture into a jug.
Carefully remove the tart shell from the tin and place on baking sheet. Pour the strained mixture into the tart shell. Very carefully slide onto the oven rack and bake for 20–25 minutes until just set. Then leave to cool.
Just before serving dust icing/powered sugar over the lemon tart using a small sieve. Serve at room temperature.