This marbled pound cake reminds me of yin and yang. Dark chocolate cake entwined with light vanilla that combines beautifully and deliciously as a whole.
Beat butter with sugar until creamy. Beat in eggs and yolk, one at a time and beating well after each addition.
Spread 1/3 of vanilla batter in bottom of loaf pan. Dollop with 1/2 of chocolate batter. Repeat with vanilla and remainder chocolate. Top with rest of vanilla batter.