In a lare saucepan, cover potatoes with cold water and bring to a boil over medium-high heat. Reduce heat and cook for 20-30 minutes, or until tender. Meanwhile, melt 2 tablespoons of the butter in a large skillet over medium-low heat. Add chopped onion and cook, stirring occasionally, until softened, 8-10 minutes. Turn heat ot medium and cook, stirring occasionally, for about 5 minutes more, or until golden.