1) Bring all the ingredients to the boil in a small saucepan and cook until the sugar has melted and the mixture thickens slightly. Remove from heat and infuse for 30 minutes. Remove ginger just before using.
For the cupcakes:
1) Preheat oven to 180C/Gas 4. Line 12-muffin tins with paper cupcake liners and spray the inside of each liner and the top of the pan with nonstick cooking spray.
2) Sift together the flour, baking powder, bicarbonate of soda, salt, ginger, cinnamon and cloves into a medium bowl.
3) Whisk together the melted butter, brown sugar, eggs, and treacle in a large bowl until blended. Add some of the water to batter then some of the dry ingredients to the batter. Continue alternating with the water and flour until everything is added and smooth.
4) Fill each mould with batter, about 1/2-cm below the top of the liner.
5) Place into preheated oven and bake until the tops feel firm and a toothpick inserted into the centre come out clean, about 15 to 18 minutes. Remove from the oven and brush the tops liberally with some of the ginger syrup.
6) Allow cupcakes to cool prior to frosting.
For the caramelised mango buttercream:
1) Heat 2 tablespoons of butter in large saute pan over high heat. Add the honey and the mangoes and cook until caramelised and soft. Transfer to a food processor and process until smooth. Pass mixture through a medium mesh sieve into a bowl.
2) In the bowl of a stand mixer fitted with a wire whip attachment, beat the egg yolks at medium-high speed until creamy and pale yellow, about 5 minutes.
3) In a nonstick saucepan, combine the sugar and golden syrup. Place over medium-high heat and bring to a full rolling boil without stirring and cook until it reaches soft-ball stage (114 to 116C) on a candy thermometer.
4) Immediately pour the mixture into a buttered measuring cup to halt the cooking.
5) Add a small amount of the syrup to the beaten egg yolks, turn on the mixer to high speed, and beat for about 5 seconds. Continue stopping the mixer, adding syrup, and beating in the same manner until all of the syrup is incorporated and the mixture is cooled completely.
6) Add the butter, 1 piece at a time, and beat until incorporated before adding the next piece. When all of the butter has been blended in, add the vanilla and slowly add the mango puree. Continue beating until combined.
Frost each gingerbread cupcake with the caramelised mango buttercream and sprinkle with the candied ginger.