Preheat the oven to 375 degrees F (190 degrees C).
Cream butter and confectioners' sugar. Mix in egg yolk, flour, and 2 tablespoons evaporated milk. Roll dough out thinly, and cut out rounds with a fluted cutter. Place into tart molds.
Bake for 12 minutes.
Beat eggs. Mix in 1/5 cup evaporated milk, custard powder, and white vinegar. Dissolve sugar in boiling water, and pour into custard mixture. Mix well, and let stand to remove air bubbles. Pour the egg custard into the baked tart shells.