1. Preheat your oven to 375⁰F (190⁰C).
2. Grease a standard loaf tin really well, especially the corners, as this cake can stick a bit.
3. In a mixing bowl, add the 1 1/2 cups Self-Raising flour, 4 oz softened butter, 2 tsp baking powder, 1 tsp vanilla essence, 3/4 cup sugar, 2 eggs, and 1/2 cup milk.
4. Beat everything together for about 3 minutes until smooth. It should look creamy and slightly thick, not runny. If it feels too stiff, add a tiny splash of milk.
5. Pour most of the batter into your prepared loaf tin, keeping back about 3 tbsp of the mixture.
6. In a small bowl, mix the reserved 3 tbsp batter with 1 tbsp cocoa powder and 1 tbsp milk. Stir until smooth and chocolatey.
7. Spoon the cocoa mixture over the vanilla batter in the tin.
8. Use a fork (or a chopstick) and gently swirl it through just once or twice. Don’t overmix or you’ll lose that marbled look.
9. Bake at 375⁰F (190⁰C) for about 50 minutes.
10. Check at 45 minutes by inserting a skewer into the centre. If it comes out clean, it’s ready.
11. Let the cake cool in the tin for about 10 minutes, then turn it out onto a rack to cool completely.
12. It slices better once cooled, though it’s tempting to cut in early.

Additional information and tips

1. You might wonder if the cake should be dense or fluffy. It’s meant to be soft but slightly firm like a classic butter cake.
2. Can I use salted butter? Yes, just skip adding extra salt.
3. Can I double it? Yes, but use a larger tin and extend the baking time.