Preheat oven to Gas 4 / 180 degrees celcius
Lightly grease a cake mold
Mix together the flour, sugar, cocoa, baking powder and salt. Add the oil, vanilla, vinegar and water. Mix together until smooth.
Pour into prepared mold and bake at 180 C for around 30 minutes.
Remove from oven and allow to cool.
Slice in half and jam generously
Melt the chocolate
Pour over the cake to decorate