I first tried these tarts when I was in Western Spain in 2007 and asked for the recipe. Here is the resulting product. They are very sweet, so you can either add lemon zest (traditional for the region) to the milk /custard mixture while its thickening to cut the sweetness or reduce the sugar.
3 Egg Yolks
1/2 cup castor sugar
2 tablespoon Cornflour
3/4 cup heavy cream
1/2 cup water
2 t-spoons vanilla essence
2 sheets puff pastry
Preheat the oven to 220c
Spray a 12 hole (1/2 cup) muffin tray with cooking spray. Into a saucepan add the egg yolks, sugar and cornflour and whisk until combined.
Slowly add in the cream and water a little at a time to form a smooth mixture. Add the large chunk of lemon zest now if desired.
Place the saucepan onto the stove on a medium heat and continue to stir. Once the mixture comes to the boil remove from the heat immediately and continue to stir. Take out the piece of rind at this stage if your using it and add in the Vanilla essence. Allow to cool slightly.
Stack the puff pastry sheets on top of each other and remove plastic sheeting.
Roll the sheets up tightly into a log and cut into 12 pieces.
Then sitting the piece on its cut side down, roll each one out on a floured surface to the size of the muffin hole. Line with the pastry to form the tarts crust, shaping into the tin with your fingers to mould the pastry.
Divide the custard mixture evenly between the pastry shells.
Bake in the oven for 20-25 minutes or until golden brown.