How to Make It
In a medium glass or stainless-steel bowl, whisk together the mayonnaise, sour cream, horseradish, vinegar, pepper, and 1/2 teaspoon of the salt until smooth.
In a large bowl, toss the escarole with the mushrooms, onion, roast beef, the remaining 1/4 teaspoon salt, and all but 2 tablespoons of the dressing. Serve the salad with the remaining dressing drizzled over the top.
• Instead of the roast beef, use leftover flaked cooked fish (salmon or any medium-firm white-fleshed fish, like cod, would be good) or use smoked fish (such as trout or whitefish).
• Add a cup of cooked broccoli florets.
• Stir in a cup or two of halved cherry tomatoes.