Sour Cream and Onion Dip

Heat oil in a 12-inch heavy skillet over medium-high heat until it shimmers, then sauté onion and shallots with 1 teaspoon salt until lightly browned, about 2 minutes. Reduce heat to medium-low and continue to cook, covered, stirring frequently, until vegetables are golden brown, about 20 to 30 minutes more. Remove from heat and stir in 1/4 teaspoon pepper and 2 tablespoons water, or enough to loosen any brown bits stuck to the bottom of the skillet. Transfer onion mixture to a medium bowl, then stir in sour cream and remaining 2 tablespoons water. (If desired, thin to desired consistency with additional water.) Stir in most of the chives, sprinkling on the rest as a garnish. Serve at room temperature.