Ingredients

1/2 cup sliced red onion 

4 teaspoons red-wine vinegar 

4 teaspoons fresh lemon juice 

4 teaspoons grainy mustard 

1/3 cup extra-virgin olive oil 

Kosher salt and freshly ground pepper 

1/2 cup finely chopped celery stalks, plus 1/4 cup chopped celery leaves 

1 pound cauliflower, cut into bite-size florets (3 cups) 

Preparation

Soak onion in water 10 minutes; drain and pat dry. In a large bowl, whisk together vinegar, lemon juice, and mustard with oil; season with salt and pepper. Stir in onion, celery stalks and leaves.

Cut 1 pound cauliflower into bite-size florets (3 cups). Steam in a pot of salted simmering water fitted with a steamer basket until tender, 7 to 8 minutes. Drain and let cool slightly; add to salad. Toss to combine, season to taste, and serve. Salad can be transferred to an airtight container and refrigerated for up to 5 days.