Step 1

Preheat the oven to 180C/160C Fan/Gas Grease and line a 900g/2lb loaf tin or 20cm/8in round tin.

Step 2

Cream the butter and sugar with an electric whisk in a large mixing bowl until very pale and fluffy. Add the beaten egg, a little at a time, whisking well after each addition. Then whisk in the vanilla extract.

Step 3

Sift the flour and salt into a large bowl, then fold it gently into the butter and egg mixture.

Step 4

Divide the cake batter into two equal portions (about 350g each).

Step 5

Add the milk to one portion of the mixture, stirring in gently until well combined.

Step 6

Mix the cocoa powder and the coffee together in a mug to form a smooth paste. Stir this paste into the other portion of the cake batter until thoroughly combined.

Step 7

Spoon large blobs of each cake mixture into the prepared tin, alternating the flavours to give a marble effect. Bake for 50–60 minutes until the cake is springy to the touch and a wooden skewer inserted into the centre of the cake comes out clean.

Step 8

Allow the cake to cool in the tin for 10 minutes, then turn out onto a wire rack and cool completely before slicing.