1. Boil potatoes until soft enough to mash. Strain most of the liquid out, leaving about 1/2 cup in the pot. The potatoes should be steaming hot.
2. Add the spinach (it will start wilting right away), margarine, and milk. Salt and pepper, to taste.
3. Mash or blend to desired consistency. I used an immersion blender which makes them silky smooth.
Source of recipe: I made it up based on mashed potatoes I had at a restaurant.