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.