01 -
Preheat oven to 170°C (338°F). Grease a 24 cm (9½-inch) round or square baking pan with butter and lightly dust with flour, tapping out excess.
02 -
In a large bowl, whisk together eggs, sugar, salt, and vanilla until pale and foamy, about 1 minute.
03 -
Slowly whisk in the vegetable oil until slightly thickened. Add the milk and whisk until smooth and homogeneous.
04 -
Sift flour and baking powder together. Add to the wet batter in two additions, folding gently with a spatula until just combined. Do not overmix.
05 -
Scoop ¼ of the batter into a small bowl. Stir in cocoa powder and 2 tablespoons of milk until fully blended.
06 -
Fold the raisins into the remaining vanilla batter to ensure even distribution.
07 -
Pour the vanilla-raisin batter into the prepared pan. Drop spoonfuls of cocoa batter on top and use a skewer or butter knife to swirl gently.
08 -
Place on the center rack and bake for 40–45 minutes, or until a tester inserted in the center comes out clean or with a few moist crumbs.
09 -
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack. Serve lukewarm or fully cooled. Optional: dust with powdered sugar or glaze.