Step 1

Preheat oven to 325°F. Spray a loaf pan with baking spray and line with parchment paper, leaving an overhang for easy removal.

Step 2

In a large bowl or the bowl of a stand mixer, cream butter and sugar 3 minutes until light and fluffy.

Step 3

Add eggs one at a time, followed by vanilla and sour cream, mixing well after each addition.

Step 4

Sift in flour and baking soda and mix gently until just combined.

Step 5

Spoon ⅓ of the batter into a separate bowl and add cocoa and hot water. Mix until just combined and smooth.

Step 6

Alternate 1/3 cup scoops of vanilla and chocolate batter into the center of prepared loaf pan until all batter is added. Tap loaf pan onto the counter a few times to minimize air bubbles, then gently swirl with a butter knife or toothpick to marble the top of the loaf.

Step 7

Bake in preheated oven for 65-70 minutes or until a toothpick in the center of the cake comes out clean. Allow to cool in pan for 15 minutes, then remove to a wire rack to cool completely.