Preheat oven to 160 degrees. Grease and flour a small loaf pan and set aside.
Put ingredients from butter to vanilla extract and beat with a hand mixer for two minutes till well blended.
Transfer half the batter into another bowl.
Whisk together the cocoa powder and hot water till a smooth paste. Allow to cool slightly, and then add into one of the bowls, mixing well till blended.
Pour in the vanilla and chocolate batters intermittently to do the marble effect. I just poured the vanilla batter and then dropped the chocolate batter over it and swirled it through using a fork.
Bake it for 50 minutes or till a skewer inserted comes out clean.
Allow to cool in pan for 5 minutes, before flipping onto a cooling rack.
Cool completely, slice and serve.