INGREDIENTS
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1 large, round loaf rustic, crusty bread
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1/4 cup real mayonnaise
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2 Tablespoons creamy horseradish sauce
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1/4 cup beef broth or stock (divided)
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salt and pepper
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2 lb. medium rare roast beef, sliced thin
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1/4 cup olive oil (divided)
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1 large yellow onion, cut into quarters and sliced (or four peeled, chopped shallots)
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16 oz. washed, sliced Portobello mushrooms
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1/2 cup dry red wine
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3 Tablespoons fresh thyme leaves
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3 large cloves garlic, minced
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3 to 4 Tablespoons grainy, country-style mustard or grainy Dijon