Cut the red and white onions into thin strips. Cut the white part of the green onions and the leeks into thin slices. Cut the green part of green onions diagonally into thin strips and place them in a container with ice water in the refrigerator.
In a saucepan over medium heat, add the butter, onions and the leeks. Cook, stirring constantly, for 10 minutes and add the water. Cook for 15 more minutes.
Blend onion mixture with NESTLÉ® Media Crema, Worcestershire sauce and sherry vinegar. Season with salt and ground black pepper.