1 1/2 pounds broccoli – cut into florets, stems peeled and sliced 1/4 inch thick
2 tablespoons white wine vinegar
2 teaspoons Dijon mustard
1/2 teaspoon prepared horseradish, or to taste
3/4 teaspoon salt
1/8 teaspoon ground black pepper
1/2 cup olive oil
3 tablespoons sour cream
3/4 pound thick sliced deli roast beef, cut into 1/2-inch pieces
2 1/2 cups cherry tomatoes, halved
6 green onions cut diagonally into thin slices
Pour 1/2 inch of water into a pan fitted with a steamer basket. Place the broccoli in the basket. Cover, and bring to a boil. Cook until tender, about 4 to 5 minutes. Drain, and cool.
To make the dressing, whisk together the vinegar, mustard, horseradish, salt, and pepper in a bowl. Continue whisking while slowly adding the olive oil to make a smooth mixture. Whisk in the sour cream.
Place the broccoli, roast beef, tomatoes, and green onions into a bowl. Stir in the dressing and toss until evenly coated. Divide the salad evenly among 4 serving plates.