- 3 tablespoons white wine vinegar
- 1 1/2 tablespoons chopped fresh tarragon
- 1 1/2 tablespoons Dijon mustard
- 6 cups fresh corn kernels
- 3 cups halved cherry tomatoes
Combine first 4 ingredients in processor. With machine running, gradually add 3/4 cup oil. Transfer mixture to medium bowl. Whisk in sour cream. Season dressing to taste with salt and pepper.
Preheat oven to 450°F. Place onions on rimmed baking sheet. Brush with remaining 1/4 cup oil. Sprinkle with salt and pepper. Roast until beginning to brown, about 10 minutes. Cool. Cut into 1-inch pieces. Transfer to large bowl.
Cook corn in large pot of boiling salted water until crisp-tender, about 4 minutes. Drain; add to onions. DO AHEAD Dressing and onion-corn mixture can be made 1 day ahead. Cover separately; chill. Add tomatoes and dressing to onion-corn mixture and toss. Serve warm or at room temperature.