1 cup cold milk
1/2 cup dark corn syrup
1 tablespoon double cream
1/2 teaspoon vanilla extract
1/2 cup confectioners' sugar
Place milk and corn syrup in a medium saucepan over medium heat and stir until smooth. Add cream and stir until thickened. Cook and stir until mixture thickens, then remove from heat and whisk in vanilla extract. Spread confectioners' sugar over the top of the cake, stirring well after each addition.
Refrigerate 4 hours or overnight, until ready to serve.