Step 1

Melt butter in a large nonstick skillet over medium; add onions, and cook, stirring often, until golden and very tender, 20 to 30 minutes. Gradually add spinach, stirring just until wilted, about 1 minute. Sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper. Remove from heat, and let stand 30 minutes.

Step 2

Stir together onion-and-spinach mixture, sour cream, and chives in a medium bowl. Stir in the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Cover and chill 30 minutes or up to 2 days. Serve with chips and veggies.