In a saucepan, combine cocoa, dark caster sugar, and boiled water.
Stir the mixture over low heat until the sugar has dissolved completely.
Set aside to cool while preparing the cake.
Preheat the oven to 180°C. Grease and line two 20cm round cake pans with parchment paper.
First, in one mixing bowl, sift together flour, baking powder, and baking soda. Set aside.Then, in a separate mixing bowl, cream together unsalted butter, granulated sugar, vanilla sugar, and a pinch of salt until light and fluffy.
Add eggs one at a time, beating well after each addition.
Gradually add the dry ingredients to the creamed mixture, alternating with the cooled cocoa syrup, and mix until well combined.
Divide the batter evenly between the prepared cake pans.Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center of the cakes comes out clean.Remove the cakes from the oven and let them cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
In a small saucepan, combine water and dark caster sugar. Bring to a boil, then reduce the heat and simmer for 5 minutes.
Add unsalted butter and chocolate drops to the saucepan. Stir until melted and smooth.Remove the saucepan from the heat and let the chocolate fudge cool slightly.
Place one cake layer on a serving plate or cake stand.Spread a layer of chocolate fudge on top of the cake layer.
Place the second cake layer on top and spread the remaining chocolate fudge over the top and sides of the cake.
Decorate as desired, and serve.