INGREDIENTS
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1 1/2 pound ground beef
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1/4 teaspoon salt
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1/3 cup crumbled blue cheese
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3 ounces cream cheese
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1 tablespoon country-style dijon mustard
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4 onion hamburger buns
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1 1/2 cup fresh mushrooms
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2 medium onions
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1/4 teaspoon salt
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1/4 teaspoon black pepper
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1 tablespoon Worcestershire sauce
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4 slices ripe tomato