To make the custard, place custard powder and sugar in a small saucepan. Add just enough milk to make a paste then add remaining milk. Slowly bring to the boil over medium heat, stirring constantly. Reduce heat and simmer for 2 minutes. Set aside to cool completely, stirring occasionally. Stir through lemon curd and rind.
Preheat oven to 180C/160C fan forced. Grease a 12 x ½-cup-capacity muffin pan.
Use electric beaters to beat butter, sugar and vanilla in a bowl until pale and creamy. One at a time add the eggs, beating well after each addition. Beat in flour and ⅓ cup of milk until well combined.
Spoon 1 tablespoon of mixture into each muffin hole, spreading slightly up the sides of the pan. Fill with 1 tablespoon of custard and top with another 1 tablespoon of batter, trying to encase the custard in batter. Repeat with remaining muffin holes.
Bake for 22 to 25 minutes, or until golden and puffed. Leave to cool for 5 minutes before turning onto a wire rack to cool. Serve dusted with icing sugar.
