Step 1: Preheat Your Oven

Start by preheating your oven to 350°F (175°C). Prepare a loaf pan by greasing it with butter or lining it with parchment paper for easy removal of the cake after baking.

Step 2: Mix Dry Ingredients

In a bowl, whisk together the flour, baking powder, baking soda, and salt. This mixture will help the cake rise and ensure a light, tender crumb.

Step 3: Cream Butter and Sugar

In a separate large bowl, beat the softened butter and granulated sugar together until the mixture is fluffy and light. This process incorporates air into the mixture, which is essential for a light cake.

Step 4: Add Eggs and Flavors

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract and sour cream until combined. The sour cream adds moisture and enhances the flavor of the cake.

Step 5: Combine the Dry and Wet Ingredients

Gradually add the dry ingredients to the wet mixture, and mix until just combined. Be careful not to overmix to keep the cake’s texture light and fluffy.

Step 6: Separate the Batter

Divide the batter in half. To one half, mix in the cocoa powder and a little orange juice for added moisture and flavor. In the other half, add the remaining orange juice and the zest.

Step 7: Create the Marble Effect

To create the marbling, alternate spooning dollops of the chocolate and orange batters into the prepared loaf pan. Once all the batter is in, use a knife or skewer to gently swirl the two flavors together. Be careful not to over-mix, as you want to maintain that beautiful marbled effect!

Step 8: Bake

Place the cake in the preheated oven and bake for 50-60 minutes or until a toothpick inserted into the center comes out clean. Keep an eye on the cake towards the end of baking time to prevent overbaking.

Step 9: Cool and Serve

Once done, remove the cake from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely. Slice when cool, and consider dusting with powdered sugar or a light glaze to enhance its presentation.