Place the potatoes in a saucepan and cover with cold water (optional: for added flavor, swap out part of water with broth, or add a spoonful of bouillon concentrated paste, such as Better Than Bouillon).
Add salt, bring to a boil, and cook just until the potatoes fall off a fork when pierced, about 20 minutes.
Drain the potatoes, and press through a potato ricer into a large bowl.
Mix in the butter, yogurt (optional), warmed LACTAID milk and chives to blend.
Add a tablespoon or 2 extra LACTAID if necessary to obtain desired consistency.