1. Heat a small skillet over medium-high heat. Add oil to pan; swirl to coat. Add onion, garlic, and 1/8 teaspoon salt; cook 4 minutes, stirring frequently. Reduce heat to medium-low; cook 6 minutes, stirring frequently. Cool onion mixture slightly.
2. Combine sour cream, mayonnaise, 1 1/2 tablespoons chives, pepper, and remaining 1/8 teaspoon salt in a large bowl. Add onion mixture; stir well. Top with remaining 1 1/2 teaspoons chives.