Chocolate pastry - Beat butter and icing sugar until fluffy, then add gradually add in vanilla extract and beaten egg and mix well.
Sift plain flour and cocoa powder together and pour into butter mixture and mix well to form into a soft chocolate dough.
Divide chocolate dough into 4 portions and place them into 4 pieces, 5 inch (12cm) round tart pans (line bottom with parchment paper). Press dough evenly into tart pan. Then prick holes on dough and bake in preheated oven at 180 deg C for 15 minutes. Remove and set aside.
Lime filling - Combine all the lime filling ingredients together, gently mix well and pass through a sift. Then pour lime liquid mixture evenly into tart pans.
Bake in preheated oven at 180 deg C for 15 mins to just set. Leave lime tarts to cool and serve or chill for 2-3 hours before serving.
Recipe by Anncoo Journal at https://www.anncoojournal.com/lime-tart/