Put everything except the egg yolks into a food processor and combine until breadcrumb consistency is achieved.
Add egg yolks until mixture forms a ball (if necessary add a small amount of water).
Cover the pastry and chill for 30 mins
Roll out, fill a 9 inch pastry case, leave to stand for 30 mins.
Cook at 200°C/fan 180°C/gas 6 for 15-20 mins until light brown.
Gently melt the butter in a saucepan.
Slice lemon, add to liquidiser with sugar, egg yolks, cornflour, & 1/2 pint of water, blitz.
Sieve into the pan of melted butter and stir continuously over a medium heat until thickened.
Continue stirring until cool, then pour into pastry case.
Whisk the egg whites adding sugar slowly.
When all the sugar is mixed and the meringue has reached soft peak, add to base and cook at 200°C until light brown.