1 tablespoon white-wine vinegar
1 teaspoon coarse-grain Dijon mustard
1/2 teaspoon salt
1/4 teaspoon sugar
1/8 teaspoon black pepper
3 tablespoons extra-virgin olive oil
1/2 pound thinly sliced cabbage (4 cups)
1/4 pound Bibb lettuce (2 to 3 heads), leaves separated and torn if large
1/4 pound mushrooms, trimmed and thinly sliced (1 1/2 cups)
4 cups loosely packed fresh flat-leaf parsley leaves (from a 1/4-lb bunch)
1 tablespoon finely chopped fresh chives
Whisk together vinegar, mustard, salt, sugar, and pepper in a large bowl, then add oil in a slow stream, whisking until emulsified.
Add remaining ingredients and toss just before serving.