Wash, peel and boil or steam potatoes until just done without making mushy.Mash the potatoes and add all the ingredients except butter.Mix them up well.Butter the bread on one side and heat the grill.Spread the aloo mixture on the side which is not buttered.Cover with another slice. Grill until done for 3 to 5 mins.Cut and serve aloo sandwich with green chutney or tomato sauce