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Ingredients

• 1 medium red onion, halved and thinly sliced
• 1 tablespoon, plus 2 teaspoons kosher salt, plus more to taste
• 6 tablespoons red wine vinegar
• 3/4 cup mayonnaise
• 3/4 cup sour cream
• 1/4 cup plus 2 tablespoons jarred grated horseradish (with liquid)
• 1/2 teaspoon grated lemon zest
• Freshly ground black pepper
• Hot sauce
• 6 Kaiser rolls
• 12 slices vine-ripened tomatoes
• 24 ounces freshly sliced rare roast beef
• 3 loosely packed cups watercress or arugula, or a combination of both

Description

Food Network