In a large heavy skillet, preferably cast iron, melt 1 tablespoon of the butter in the vegetable oil. Add the onion and red and green peppers and cook over moderately high heat, stirring, until wilted, about 4 minutes. Mix in the potatoes and press into an even layer in the skillet. Cook over moderate heat until browned and crusty on the bottom, about 5 minutes. Season with salt and pepper. Turn the potatoes, adding the remaining 1 tablespoon butter to the skillet as you turn, and cook until well browned, about 5 more minutes. Season with salt and pepper and serve with hot sauce.