People tend to get excited about this beloved dip, especially when it's made from scratch. The caramelized onions give it a nutty finish. The secret to this luscious onion dip is mixing low-calorie Greek yogurt with a smaller amount of sour cream.
Heat oil in a large nonstick skillet over medium heat. Cook onions with 2 teaspoons salt, stirring often, until caramelized, 35 to 40 minutes.
Add water; cook, scraping any brown bits from bottom to deglaze skillet. Transfer onions with brown bits to a medium bowl; let cool for 30 minutes.
Stir yogurt, sour cream, lemon juice, and cayenne into onions. Refrigerate for at least 1 hour. Sprinkle with cayenne. Serve with vegetables.
Storage: Dip can be refrigerated for up to 2 days.