Mix the flour, icing sugar and salt in a bowl. Now with your hand mix in the butter to get a crumb like mixture.
Add 3 tbsp of cold water. Let it come together well to make a dough. Chill for half an hour.
Grate the zest of the oranges and squeeze out the juice of all 3 oranges.
In a food processor, add the zest of the orange with sugar and process for 2 minutes.
Add in the butter and process till you get a cream like consistency.
Add the eggs gradually followed with orange juice and salt, combine well.
Heat a saucepan over low heat, add this mixture and stir consistently until it begins to thicken. Remove from heat.
Roll out the dough into the tart mould and bake at 200°C for 20 minutes. Let this cool and remove from mould.
Pour in the orange curd mixture into the tart shells, place a slice of lemon slices. Refrigerate for 1 hour.
Serve when chilled