In a large bowl, whisk together 1 1/2 teaspoons grainy mustard, 1 tablespoon plus 1 1/2 teaspoons white-wine vinegar, 1 teaspoon honey and 1 tablespoon extra-virgin olive oil. Season with coarse salt and freshly ground pepper. Add 1/2 pound brussels sprouts, trimmed and shredded; 1/2 small head radicchio, cored and thinly sliced; 1/4 cup snipped fresh chives, and 2 tablespoons toasted sunflower seeds. Toss to combine and seve.
