Heat a large pan over medium-high heat. Add oil, onions, 1 teaspoon salt and cook for 15 minutes. Reduce heat to low and cook 40 minutes more until onions are meltingly tender and caramelized.

Remove from pan and blend in a food processor or blender, with vinegar, honey and mayonnaise. Season with salt and pepper.

Garnish with crispy onions and chopped parsley. Store in covered container in the refrigerator for a week.