Supermoist chocolate cake

This cake is one of my favorites. It's the one I always make for birthdays and dinner parties. It's a winner, and you can't go wrong with it. And you can absolutely mistake this cake for being a regular cake filled with eggs and milk.
I have wrote down two different toppings, you can choose which one you want, they are both really good.  I have used the first one on this picture.

RECIPE

400 grams sugar
375 grams flour
55 grams cocoa powder
2 tsp baking soda
4 3/4 dl water
1,5 dl oil
1 tsp vanilla extract
2 tsp vinegar (I use apple cider vinegar)

Topping 1:
200 grams vegan butter, softened
2 tbsp cocoa powder
5 dl powdered sugar

Topping 2:
200 grams dark chocolate, melted
3-4 tbsp vegan butter
1 tsp vanilla sugar

Cake:
Mix together the dry ingredients in one bowl, and the wet ingredients in another bowl. Combine them and stir until you have a smooth batter. Pour the batter into a cake pan (I use a rectangular pan, about 20 x 30 centimeters). Put the cake in the oven on 350 F for about 30 minutes. Let it cool while in the pan.

Toppings: for the first one, just put everything in a food processor and blend it smooth. Use a spatula and smooth it nicely over the cake.
For the other topping, melt the chocolate (the microwave does this easy and fast), stir in the soft butter and the vanilla and pour it over the cake. Let it cool completly before cutting it up in squares.