Turn the oven on 160 degrees celcius fan.
Start by making the cake. Stir the apple cider vinegar into the oat cacao.
Melt butter, syrup and coffee at low heat.
Mix flour, cacao powder, sugar, salt, baking soda and baking powder and sift it into a large bowl.
Stir in the butter mixture.
Chop the chocolate and stir it in the dough.
Line a 22 x 22 cm ting with a baking sheet and pour in the dough.
Bake the cake for 30-35 minutes until a pin comes out clean when sticking it into the middle of the cake.
Let the cake cool completely.
When the cold is cold, whip the ingredients for the frosting together. It might be dry at first but it will and should end up creamy, light and airy.
Spread out the forsting on top of the cold cake and top with flakes of sea salt.