Simmer potatoes and turnips in 1 1/2 inches water in a large covered saucepan until tender (about 20 minutes).
Drain vegetables; reserve cooking liquid.
Puree vegetables with milk solids, milk, salt, pepper, and butter in a food proces...
Simmer potatoes and turnips in 1 1/2 inches water in a large covered saucepan until tender (about 20 minutes).
Drain vegetables; reserve cooking liquid.
Puree vegetables with milk solids, milk, salt, pepper, and butter in a food processor or blender.
Add reserved cooking liquid and mock creme fraiche, if used, for desired consistency.
Return mixture to saucepan and heat thoroughly.