Add the potatoes and carrots to a large pot of boiling water and cook until they are easy to pierce with a fork, about 10 minutes. Drain the potatoes and carrots and put them in a bowl or food processor.
Heat the olive oil in a large saute pan, add the onions and cook until tender, about 7 minutes. Add the scallions, garlic and chiles and cook 3 minutes longer.
Mix the Sauteed ingredients with the potatoes and carrots. Add the butter and sour cream. Blend well until the hot potato mixture is creamy but firm. Use milk, half-and-half, or mocha mix to reach a thick and creamy consistency. Season to taste with salt and pepper. For spicier potatoes add serrano chiles