If you work the back and the biceps on the same day then try this one out. I like to save this towards the end of the work out when I'm doing a few sets of biceps. If you're doing a good job of exercising your back and you don't need a lot of biceps work at the end. I find that 3-5ish total sets of biceps are plenty.
Pick a wait for barbell curls that you can do about 6-8 times. Make sure that your reps look good. For this particular exercise there's no need to cheat any.
After you've done your barbell curls, immediately lean over into a rowing position. Now you will be in a position to do underhanded barbell rows. You'll find that this isn't a lot of weight to do rows with but the point is your biceps are already tired. So think of it still as a biceps exercise rather than a back exercise. Your back is just helping your biceps work more. Finish the exercise by doing however many reps you feel appropriate. Your biceps should be burning like crazy.