Steak Sandwiches with Horseradish Mustard Butter and Watercress

Ingredients

• 1 large bunch watercress
• 1 20- to 22-inch baguette
• 1 1-lb piece flank steak (3/4 to 1 inch thick)
• 1 ½ tablespoons shallot
• 3 tablespoons Dijon mustard
• 3 tablespoons bottled horseradish
• 6 tablespoons unsalted butter

Preheat broiler. Blend together butter, horseradish, mustard, shallot, and salt and pepper to taste in a bowl with a fork until combined well. Pat steak dry, season both sides well with salt and pepper, and put on rack of a broiler pan. Spread top of steak with 1 tablespoon mustard butter, then b...

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