1 small head of cauliflower (about 1 3/4 pounds)
1 teaspoon coarse kosher salt
6 tablespoons (3/4 stick) butter
2 tablespoons fresh lemon juice
2 tablespoons whole grain Dijon mustard
1 1/2 teaspoons finely grated lemon peel
1 tablespoon finely grated lemon peel
DO AHEAD! This lovely side dish can be made 2 hours ahead. Let stand at room temperature. If desired, rewarm in 350°F oven until heated through, about 10 minutes.
Transfer cauliflower to a platter. Sprinkle with parsley and serve warm or at room temperature.