Preheat oven to 180°C bake.
Prepare a 24cm loose bottomed quiche/cake tin.
Combine Chelsea White Sugar and one egg in a food processor until pale and frothy. Add butter, flour, baking powder and salt.
Process until mixture clumps together in a ball around the blade. If dough is a little dry, add 1 Tbsp chilled water. Wrap dough in baking paper and chill for 30 minutes, then press into the base and up the sides of the prepared quiche or cake tin. Chill again for 30 minutes.
Place a sheet of baking paper on top of pastry and fill with dry rice or baking weights. Blind bake for 15 minutes, until golden and crisp. Leave oven on. Whisk remaining egg and brush over pastry base while still hot.
While pastry is cooking, combine cornflour, lemon zest and juice in a saucepan. Mix until smooth. Add egg yolks, Chelsea White Sugar, water and butter. Cook gently, stirring until mixture thickens like custard (about 10 minutes). Set aside.
Beat egg whites until stiff peaks form. Gradually beat in Chelsea Caster Sugar or Chelsea Raw Caster Sugar until all incorporated and mixture is glossy. Pour filling onto cooked pastry then pipe or pile meringue on top.
Bake for 15-20 minutes, until meringue is firm and golden. Cool in tin.
Remove when cold and serve with whipped cream or ice cream.