Actually, milk paint is one of my "unventions". It appeared in a recent issue of Technique Junkies newsletter. If you're interested in subscribing to this wonderful publication, just go to
http://www.patstamps.com.
To do the technique, you need cardstock, an ink pad and marker in the same color as the cardstock, and a white or vanilla craft pad. Swipe the craft pad across the cardstock in one direction and let it dry. Then swipe the pad of the same color as the cardstock in the same direction and let it dry. Then add your plank lines with the marker, if you wish.
Milk paint is a finish used on furniture in the past and present and actually comes in a number of different colors, so you needn't limit yourself to just brown shades!