This salad dressing is known in the USA as thousand island salad dressing. What is the recipe? I have learned that mixing ketchup with mayo does the trick, but the taste is not as fresh..and always ends up tasting more sweet than I like it. I like this dressing in salad with boiled eggs, green olives, tomato, lettuce and cheddar.
Marie Rose Sauce, also known as Thousand Island Dressing is traditionally made from a mixture of ketchup and mayonnaise. Marie Rose is usually associated with prawn/shrimp cocktail and Thousand Island often used in a Reuben sandwich. If you find this mixture to be too sweet then you can try switching some of the ketchup for tomato puree/paste which has a stronger tomato flavour. However you may find this to be a little too harsh or salty in which case there are ways to adapt the traditional recipe to a slightly fresher, more modern form. You can lighten the mixture by adding some plain yogurt to the mayonnaise. Our preference would be to use a 50/50 mixture of Greek-style yogurt and mayonnaise and then add ketchup to taste. You can use a lower fat variety of Greek-style yogurt (such as 2% fat) to make the mixture less heavy.
You can also brighten the flavour of the dressing by adding a good squeeze of lemon juice, a few shakes of Tabasco or hot sauce, a dash of Worcestershire sauce (Lea & Perrins) and even a little grated horseradish (fresh or from a jar). To add a bit of variety you can add some finely chopped gherkins/cornichons/dill pickles or pimentos which would make it more like a Russian Dressing, and some people like to add grated onion to the mixture too.