Preheat oven to 180 deg Celsius. In a large bowl, melt the 125g butter, add the hot water, oil and cocoa and mix well with a whisk
Sift in the flour and add the sugar. Mix the half cup buttermilk with the 2 eggs and add to the mixture. Mix it well ensuring there are no lumps
Pour mixture into a glass ovenproof dish, I used a 300mm x 220mm dish, lined with parchment paper or a baking pan and bake at 180 degrees celcius for 25-30 minutes
In the meantime mix the 70gram melted butter with the 3 tablespoon buttermilk,1 teaspoon vanilla, 2 tablespoon cocoa and the icing sugar. Use a whisk and mix into a smooth, velvety liquid.
Whilst cake is still warm prick a few wholes into the cake and pour the liquid icing over the cake. Place cake in the fridge for at least 45 minutes to cool down before cutting into squares.