Wash and peel Jerusalem artichokes; slice.
In covered pan cook in a small amount of boiling salted water till tender, 10 to 15 minutes.
Melt butter in a saucepan; blend in flour, salt, and white pepper.
Add cream or milk all at once.
Cook and stir till thickened and bubbly.
Remove from heat.
Stir in snipped parsley.