Preheat your oven to 180°C (350°F). Grease a loaf pan and line it with parchment paper for easy removal.
In a large mixing bowl, cream together the softened butter and sugar using an electric mixer until the mixture is pale, fluffy, and fragrant—about 3-4 minutes. This creates a smooth, airy base.
Add eggs one at a time, beating well after each addition. The batter may look a little curdled, but that’s normal and will come together in the next steps.
Stir in the vanilla extract. In a separate bowl, whisk together the sifted flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with the milk. Mix on low speed just until combined, being careful not to overmix.
Divide the batter evenly into two bowls. In one, fold in the cocoa powder until smooth—this will be your chocolate batter for swirling.
Drop spoonfuls of vanilla and chocolate batters into the prepared loaf pan, alternating between the two. Use a toothpick or skewer to gently swirl through the batters, creating a marbled pattern—don’t overmix, keep it loose.
Bake in the preheated oven for about 50-55 minutes. Check doneness by inserting a toothpick into the center—the cake is ready when it comes out with moist crumbs and the top is golden.
Remove the cake from the oven and let it cool in the pan for 15 minutes. Then, transfer it to a wire rack to cool completely—this helps set the pattern and prevents sogginess.
Once cooled, slice the cake with a serrated knife to reveal the beautiful marbled pattern inside. Serve at room temperature and enjoy the tender crumb and striking visual contrast.
