Line a 12-section bun tray with paper or foil cake cases. Put the butter, maple syrup and muscovado sugar in a saucepan and heat gently, stirring, until the butter has melted. Mix together the flour, baking powder and ground ginger in a bowl. Beat together the eggs and milk in a separate bowl.
Take the butter pan off the heat, then beat in the flour mixture. Gradually beat in the egg and milk mixture, then stir in the glacé ginger. Divide the cake mixture between the cake cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 10–15 minutes or until well risen and cracked. Transfer to a wire rack to cool.
Sift the icing sugar into a bowl and gradually mix in the water to create a smooth, spoonable icing. Drizzle random lines of icing from a spoon over the muffins and decorate with slices of glacé ginger. Leave to harden for 30 minutes before serving.