Preheat oven to 425°F.

Place scallions on a baking sheet. Toss with olive oil.

Roast at 425°F for 15 minutes. Reserve ⅓ cup of the roasted scallions for topping. Allow scallions to cool a bit before blending.

Blend remaining scallions in a food processor with olive oil, mayonnaise and red wine vinegar. Blend until smooth. Serve with reserved roasted scallions, and a drizzle of olive oil.

Store in covered container in the refrigerator for up to a week.