1-First Step: Prepare the base batter. In a large bowl, cream 1 cup softened butter and 2 cups sugar until light and fluffy, about 3-5 minutes with an electric mixer. This builds air for a moist marble cake. Add 4 eggs one at a time, beating well after each. Mix in 1 tsp vanilla extract. For vegan, use applesauce here.

2-Second Step: Combine dry ingredients. In a separate bowl, whisk 3 cups flour and 1 tbsp baking powder. Alternate adding dry mix and 1 cup milk to the wet ingredients, starting and ending with dry. Mix on low until just combined, avoiding overmixing for tenderness. Gluten-free flour works seamlessly.

3-Third Step: Divide and flavor the batters. Split batter evenly into two bowls (about 3 cups each). To one, stir in 1/4 cup cocoa powder and 2 tbsp milk until smooth. This creates the chocolate half. Taste for balance; low-calorie version uses less sugar here.

4-Fourth Step: Layer and swirl. Spoon vanilla batter into the prepared pan. Add chocolate dollops on top, alternating sections. Use a knife or skewer to gently swirl from center to edges, creating ribbons without muddying colors. Two or three passes suffice for a pretty swirled cake.

5-Fifth Step: Bake to perfection. Place in the oven for 50-60 minutes. Test with a toothpick in the center; it should come out clean or with moist crumbs. Cool in pan 10 minutes, then invert onto a wire rack. Full cool prevents crumbling.

6-Sixth Step: Glaze and serve. Whisk 1 cup powdered sugar, 2 tbsp cocoa, 2-3 tbsp milk, and 1/2 tsp vanilla for icing. Drizzle over cooled cake. Slice to reveal swirls. Pairs with coffee or fruit. For busy schedules, batter preps ahead.