1Place sun-dried tomatoes in a small bowl. Pour 1/4 cup boiling water over tomatoes and let soak for 10 minutes. Remove tomatoes and reserve the soaking liquid. Finely dice tomatoes. combine tomatoes, soaking liquid, mayonnaise, buttermilk, vinegar, garlic, sugar, and oregano in a food processor. Whirl until smooth. Store in a jar in the refrigerator.