Line a 7 inches (18x18 cm) square pastry ring with baking paper and set aside.
Put flour, icing sugar, and salt into a food processor bowl, process to combine.
Put the butter into the bowl.
Process until fine crumbs formed.
Pour into the prepared pan, and press to level the top, refrigerate for 30 minutes.
Heat fan oven at 325F-160°C.
Bake for 20 minutes, leaving the shortbread inside the mould.
Put egg, egg yolks, sugar, salt and lemon zest into a saucepan, whisk to combine.
Put the butter into the saucepan.
Place over low heat, and cook until thickened.
Pass through a sieve into a jug.
Pour the whipping cream into the jug.
Stir to combine.
Pour into the hot base.
And bake for 10-15 minutes more.
Let it cool completely before refrigerating.
Remove the ring, sprinkle with icing sugar before cutting into pieces.
Recipe from Deliciousdays.com