Preheat the oven to 180°C and line a muffin tin with paper cases.
Melt the butter in a pan and beat with sugar, oil, arrowroot, and vanilla.
Whisk in the eggs, milk, and cream until the mixture is combined.
Sift and beat the flour and baking powder into the mixture in batches.
Spoon the batter into cases and bake for 20-25 minutes until springy.
Mix icing sugar, glucose, condensed milk, flavoring, and butter until smooth.
Beat in the baking margarine until the consistency is light.
Dissolve icing sugar into the cream and add optional food coloring.
Gradually beat the cream mixture into the butter mixture until fluffy.
Pipe the icing onto cooled cupcakes starting from the edge in a spiral.
Finish with a quick upward pull at the center and add sugar sprinkles.