In 12-inch nonstick skillet, melt 1 tablespoon butter over medium-high heat. Stir in onion slices to coat with butter. Cook uncovered 10 minutes, stirring every 3 to 4 minutes. Reduce heat to medium-low. Sprinkle with salt. Cook 10 to 15 minutes longer, stirring every 5 minutes, until onions are golden brown. Remove from skillet; cool slightly. Chop onions.