Typically, yams have a tough, scaly skin, while sweet potatoes have smooth skin. True yams have skin that looks something like tree bark. Their flesh can be white, yellow, reddish, or purple.

Purple sweet potatoes are also very distinct in their heritage and growing regions. A handful of purple varieties thrive in the United States; some more readily available than others.

Yams, for one, grow on vines, while sweet potatoes grow underground. Ube is often confused with Stokes Purple sweet potatoes or Okinawan sweet potatoes. Advertisement. Advertisement.

Mash the yams and potatoes. In a different pan, over medium-low heat, combine milk + ½ stick of butter until the butter is melted. Add butter and milk mixture to potatoes and yams.