Marble Cake (Chocolate & Vanilla Swirl)

Steps

1. Preheat the oven to 175°C (350°F). Grease a 23 cm (9-inch) round cake pan, line the bottom with parchment paper, and lightly grease the parchment.
2. In a medium bowl, whisk together the all-purpose flour, baking powder, and fine salt until evenly combined and lump-free.
3. In a large mixing bowl, beat the unsalted butter at 20–22°C with the granulated sugar for 3–4 minutes, until very pale, creamy, and fluffy with a lighter texture.
4. Add the eggs one at a time, beating well after each addition and scraping down the sides of the bowl. The mixture should look smooth, slightly thickened, and glossy with no streaks of egg.
5. In a small jug, combine 160 ml of the whole milk (reserving 30 ml) with the vanilla extract. Make sure this mixture is at about 20–22°C.
6. Add one-third of the dry ingredients to the butter mixture and mix on low just until incorporated. Add half of the milk–vanilla mixture and mix briefly. Repeat, alternating dry ingredients and liquid, finishing with the last third of the dry ingredients. Mix only until a smooth, thick, creamy batter forms with no visible dry flour. Do not overmix to keep the crumb soft and tender.
7. Weigh or visually divide the batter evenly between two bowls. In a small bowl, whisk the cocoa powder with the reserved 30 ml whole milk until smooth and lump-free, then stir this cocoa mixture into one bowl of batter until it is evenly chocolate-colored and silky.
8. To create the marble effect, spoon alternating large dollops of vanilla and chocolate batter into the prepared pan. Once all the batter is in, use a thin knife or skewer to gently swirl through the batter in a few figure-eight motions, creating clear ribbons without overmixing the two colors.
9. Bake for 30–35 minutes at 175°C (350°F), until the top is lightly golden, the edges pull just slightly away from the pan, the center springs back when gently pressed, and a toothpick inserted in the center comes out clean or with a few moist crumbs but no wet batter.
10. Place the pan on a wire rack and let the cake cool in the pan for 10–15 minutes. Then carefully turn it out, remove the parchment, and let it cool completely on the rack to 20–22°C before slicing. The finished cake should have a moist, tender, fine crumb with distinct chocolate and vanilla swirls and a softly golden, even crust.