INGREDIENTS
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1 1/2 lbs ground beef
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1/2 cup Panko bread crumbs
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1 egg
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1/4 teaspoon black pepper
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1 tablespoon all-purpose flour
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1 1/2 cups beef broth ((low sodium))
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1 oz package brown gravy mix ((dry))
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2 tablespoons ketchup
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1 teaspoon dijon mustard
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2 tablespoons butter
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1 onion (, thinly sliced)
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1 cup mushrooms (, thinly sliced)
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2 tablespoons cornstarch
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4 tablespoons water
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6 large rolls or Kaiser buns
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6 slices swiss or cheddar cheese