Preheat oven to 180°C. Grease or line a 12 x 1/3-cup capacity muffin pan with paper cases.
Combine flour and sugar in a bowl. Add butter, eggs, milk and vanilla. Using an electric hand mixer, beat mixture for 2 to 3 minutes or until well combined and pale in colour. Spoon heaped table-spoonfuls of mixture into paper cases.
Bake for 12 to 15 minutes or until a skewer inserted into centre comes out clean. Transfer to a wire rack to cool.
Using a small, sharp knife, cut a shallow disc from centre of each cake, 1cm in from edges and 1 1/2cm deep. Cut discs in half to form butterfly wings. Fill cavity of each cake with lemon curd. Arrange 'wings' in lemon curd. Sprinkle with icing sugar before serving.