Onion, cooked until soft, golden, and sweet, gives this low-fat appetizer dip an extraordinary flavor. For a healthy snack that's ready when you are, make an extra batch and keep in the refrigerator with cut up vegetables.
Cut onion in half, then thinly slice. Cut the slices in half. Heat oil in a medium-size nonstick skillet over medium-low heat. Add onions and thyme to pan and cook, covered, stirring occasionally for 25 minutes, or until golden-brown. Remove cover, cook 5 minutes. Allow to cool.
While onions cook, whisk together mayonnaise, sour cream, salt and pepper.
Once onions have cooled, stir into mayonnaise mixture and refrigerate for 1 hour. Serve with raw vegetables.