Place edamame in a medium saucepan. Add water to cover 2 inches above edamame; bring to a boil. Cook 7 to 8 minutes or until soft; drain and set aside.
. Place potato in same pan; add water to cover. Bring to a boil; reduce heat, and simmer, uncovered, 8 minutes or until tender. Drain, reserving 1/4 cup cooking liquid.
. Place edamame and reserved cooking liquid in a food processor or blender; process until smooth. Combine pureed edamame, potato, milk, and remaining ingredients in a large bowl. Mash with a potato masher until desired consistency.