To make the tart dough, place the butter in a large food processor bowl fitted with a metal blade. Process until smooth and creamy, scraping down the sides with a rubber spatula as needed.
Add the icing sugar and process until well blended.
Add the ground almonds, salt, vanilla and process until smooth, scraping down the sides of the bowl as necessary before adding the egg and processing until combined.
Add the flour and pulse the mixture until it just starts to form a ball and stop. Remove the mixture from the food processor bowl and place onto cling film and form into two flat discs. Wrap each disk separately and refrigerate for at least 4 hours, you can freeze the 2nd dough disk to use another time.
Once chilled, remove the dough from the refrigerator and roll out between 2 sheets of baking paper until 3mm thick.
Carefully place the dough into a 24cm tart tin and press the dough against the bottom and edges of the tin to ensure it is well fitted. If the dough cracks or splits simply patch with additional pastry. Trim the top of the tart – the easiest way to do this is to roll the rolling pin over the top of the tart case which will trim the edges neatly.
Refrigerate for at least 30 minutes and repeat with the second portion of dough.
Preheat the oven to 180 degrees celsius (350 Fahrenheit) and line the tarts with baking paper and add dried beans or pastry weights and bake for 20 to 25 minutes until lightly coloured.
Set aside while you make the filling.
To make the filling, preheat the oven to 150 celsius (300 Fahrenheit) whisk the eggs and caster sugar in the bowl of an electric mixer until well combined. Whisk in the lemon zest and juice before sifting the flour over the top and whisking until smooth.
Pour the filling into the prepared tart cases and bake for 20 to 25 minutes, or until the top is set.
Once cool dust with icing sugar.
Makes 2 tarts. If you want to make 1 tart you can safely scale down the filling, and freeze the unused portion of tart dough.