Preheat the oven to 500°. In a large, heavy skillet, cook the bacon over moderate heat until lightly browned around the edges, about 3 minutes; drain. Add the onion to the skillet and cook over moderate heat until lightly browned, about 2 minutes. Add the potato and cook, stirring, for 3 minutes; add a little water to the pan if the potato begins to stick. Stir in the vinegar, chives and sage and season with salt and pepper; remove from the heat.