In a large heatproof bowl, mix the eggs, extra yolks, sugar, lemon zest and juice.
Place the bowl over (but not touching) a saucepan of gently simmering water and stir constantly for 5 to 10 minutes until the mixture is thickened and custard-like.
Strain the mixture through a sieve into a small bowl to make sure there are no lumps and then cover with cling-film and refrigerate for 1.5 hours.
For the pastry case, cream the butter and sugar together in a bowl. Then beat in the 3 egg yolks, one at a time.
Mix in the flour until the mixture forms a solid dough.
Tip the dough out onto a floured work surface and knead briefly until smooth, then wrap in