Preheat your oven to 160 C / 325 F. Butter a 9 x 5 loaf pan well and dust with flour.

In a bowl, whisk together the flour, salt and baking powder.

Cream together the butter and sugar using a hand held mixer or a wooden spoon until light and creamy. This will take 5-10 minutes with a handheld mixer.

Add the eggs , one by one , and beat well after each addition.

Add the vanilla and beat for a minute.

Add a third of the flour mixture , beat until incorporated .

Add half of the milk and beat until smooth.

Repeat with a third of the flour mixture, then the remaining milk and then the last of the flour mixture , beating well after each addition.

Take a little less than half of the batter into another bowl. Add and beat in the cocoa powder until smooth.

In your prepared pan , spread some of the vanilla batter . Using a spoon add dollops of the chocolate batter. With a knife or skewer, swirl the chocolate into the vanilla.

Spread more vanilla batter on top and keep repeating the swirling with the chocolate until you use up all your batters.

Bake at 160 C/ 325 F for 45-55 minutes until the cake springs back when pressed gently or a skewer inserted in the centre comes out dry.

Cool in pan for 10 minutes and then unmould the cake onto a wire rack and cool completely