1. Make the chocolate cake:
Preheat the oven to 170°C (gas mark 5-6) preferably using the fan setting.
Pour the cake mix into a large mixing bowl. Add the eggs and melted butter. Using the whisk, beat until you have a smooth, lump-free texture. Pour the batter into the buttered and floured cake tin (12 cm diameter) and bake in the middle of the oven for 45 min.
After the recommended baking time, insert a knife or skewer into the centre of your cake, if it comes out clean and dry your cake is ready. Turn out the cake after it has cooled completely.
2. Make the mascarpone butter cream:
In a large mixing bowl, beat the softened butter with the icing sugar and vanilla until the mixture becomes pale and fluffy. Add the lemon juice and continue to beat for 2 minutes. Add the mascarpone using the spatula.
Once the cake has completely cooled, slice it into four layers. Make a hole in the middle of two of the layers. Place a layer without a hole on a cake stand. Cover with the butter cream and then add a layer of cake with a hole. Cover with the cream and a second layer with a hole. Fill the hole with the sugar-coated chocolate sweets and then spread some cream over the cake and close with the last layer without hole. Cover the entire cake in the butter cream and refrigerate for 30 minutes.
To finish, carefully roll the cake in the sugar sprinkles until is entirely covered.