Heat oven to 325 degrees F.
Season ribs with salt and pepper. Heat nonstick skillet over medium-high heat. Working in batches, brown ribs, 7 to 10 minutes. Put in large, deep ovenproof pot.
In same skillet, heat oil over medium-high. Add leeks; saute until browned, 8 minutes. Add 2 cups nectar, tequila, broth and chipotle; simmer 1 minute. Pour over ribs.
Bake, covered, in 325 degree F oven 3 hours or until ribs are very tender; turn ribs over every 45 minutes.
Remove pot from oven. Let ribs cool in sauce, uncovered, 30 minutes. Remove ribs from sauce and refrigerate, covered, overnight. Cover sauce in pot and refrigerate overnight.
To serve, discard fat from sauce. Add remaining 3 tablespoons nectar, ribs to sauce. Reheat over medium heat, 20 minutes. Top with scallion. Makes 12 servings.