1. 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.
2. 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.
Variations:: · 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.
Wine Recommendation: Wine lovers revere merlot for its soft, supple texture and seductive plum and chocolate flavors. Versions from Washington State have an added earthy note that will marry well with this dish.