Ingredients

• 1/4 cup white wine vinegar
• 1 teaspoon Dijon mustard
• 1/3 cup olive oil
• Coarse kosher salt
• 1 pound Treviso (about two 8-ounce heads)
• 4 cups (packed) mixed baby greens or other baby lettuces (about 3 ounces)
• 1/4 cup chopped fresh chives
• 1 cup (packed) coarsely grated Gruyère cheese (about 4 ounces)
• 1 cup walnut halves, toasted

Instructions

1. Whisk vinegar and mustard in small bowl to blend. Gradually whisk in oil. Season dressing to taste with coarse salt and freshly ground black pepper.
2. Cut Treviso crosswise into 1/2-inch-wide strips; discard bottom 2 to 3 inches. Place strips in large bowl; add mixed baby greens and chives. DO AHEAD: Dressing and salad can be made 6 hours ahead. Cover separately and chill. Bring dressing to room temperature and rewhisk before using. Pour dressing over salad and toss to coat. Add cheese and walnuts; toss salad, then transfer to serving bowl.