Peel and dice potatoes, place in large saucepan. Add enough water to cover and bring to a coil. Reduce hat and simmer for 10-15 minutes until tender.
Place potatoes in large bowl. Beat until smooth. Add all remaining ingredients except chiles. Fold in until butter is melted. Fold in chiles.
To roast chilies, line broiler pan rack with foil & cut holes in foil. Cut chiles in half and remove seeds. Place cut side down on foil-lined pan. Broil 4-6 inches from heat for 8-10 minutes until skims are charred. Place chiles in paper bag for 10 minutes. Peel and discard skins. Coarsely chop chiles.