Lamingtons

Name: Lamingtons
Prep time: 40 min
Cook time: 35 min
Total time: 1 h 15 min
Cuisine: Australian
Ingredients: 185 g (1 ¼ cup) plain flour (all-purpose flour); 2 teaspoons baking powder; 40 g (⅓ cup) cornflour (US: cornstarch); 200 g (2 sticks minus 1 tablespoon) unsalted butter, softened; 230 g (1 cup plus 1 tablespoon) caster sugar (superfine sugar); 2 teaspoons vanilla extract; 3 eggs; 125 ml (½ cup) full cream milk (whole milk); 500 g (3 ⅔ cup) icing sugar (powdered sugar), sifted; 200 g (7 oz) dark chocolate (bittersweet chocolate, 60% or 70% cocoa content); 15 g (1 tablespoon) unsalted butter; 125 ml (½ cup) milk, plus more; 325 g (12 oz) dessicated coconut (shredded coconut)