You know those delightful chocolate oranges by Terry's? A whole chocolate orange splits into milk chocolate, orange-scented wedges that are just wonderul (and a traditional holiday gift). The Terry's orange is always a welcome sweet treat but really divine, if you coarsely chop one up and add it to this tender, buttery cake. You can marbleize this cake or leave it as a vanilla-orange batter, with the Terry's Orange pieces, flecked throughout the cake. This cuts into thick, moist slices of cake - not as heavy as most pound cakes and richer than a quick bread.