Step 1
Preheat oven to 18º0 C. Grease a loaf tin with some butter and dust with some flour.
Step 2
Cream together butter and castor sugar in a bowl with an electric beater. Add eggs gradually and whisk well. Add vanilla essence and whisk.
Step 3
Sieve together flour and baking powder into the mixture and fold in well. Divide the batter equally into 2 different bowls.
Step 4
Take cocoa powder in a bowl. Add oil and mix well.
Step 5
Add cocoa-oil mixture to one portion and mix well. Add coffee decoction to the other portion and mix well.
Step 6
Pour ½ of coffee batter into the loaf tin and put cocoa batter on top. Put remaining coffee batter on top, insert a fork and swirl to create marble effect, level it out and tap.
Step 7
Place the tin on a baking tray, place the tray in the preheated oven and bake for 25-30 minutes. Remove from oven, cool and demould.
Step 8
Dust with icing sugar and slice. Serve.