Rib the butter or margarine into the
flour and sugar until the mixture resembles breadcrumbs. Work in the
egg yolks until well blended. Cover with clingfilm (plastic wrap) and
chill for 1 hour. Roll out two-thirds of the pastry (paste) and use to
line greased tartlet tins (patty pans). Fill with the custard filling.
Roll out the remaining pastry and cut out lids for the tarts. Moisten
the edges and press them together to seal. Bake in a preheated oven at
200°C/400°F/gas mark 6 for 15–20 minutes until golden. Leave to cool
in the tins.