For base: Beat Butter and Icing sugar together untill it forms a creamy paste..
Add egg yolk and few drops of vanilla essence n mixx well....then add plain flour in this mixture. Rub and make sure not to mix it too much

Roll the dough out on a flat, lightly floured surface make almost 15 rounds (3inches in diameter) out of it
Put them in a muffin tray and bake in preheat oven 15 to 20 mins (it depend on clr) on 180°

For filling: Mixx all the above ingredients except butter and lemon juice..in a sauce pan
Cook it on low flame..whisk gently until the mixture bcomes thicken
Then add lemom juice and butter..mix well
Allow the mixture to cool before filling it in the baked cases
Place the tarts in fridge for cooling<
Served chilled... :)