For the Vanilla Cake Batter

• 3 cups all-purpose flour
• 2 teaspoons baking powder
• ½ teaspoon baking soda
• ½ teaspoon salt
• 1 cup unsalted butter, softened
• 1¾ cups granulated sugar
• 4 large eggs, at room temperature
• 1 cup sour cream (or Greek yogurt)
• 2 teaspoons vanilla extract
• ¼ cup milk

For the Chocolate Swirl

• ⅓ cup unsweetened cocoa powder
• ¼ cup hot water or hot milk
• 2 tablespoons granulated sugar (optional, for deeper chocolate flavor)

For Finishing (Optional but Recommended)

• Powdered sugar, for dusting
• Chocolate glaze or vanilla glaze
• Fresh berries or whipped cream for serving