"Philly style steak cooked with onions, mushrooms, bell peppers, and garlic smothered in a fantastic and easy horseradish cheese sauce and then grilled on sourdough bread...."
INGREDIENTS
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For the Steak:
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1 pound flank steak, still partially frozen (see note)
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1 tablespoon Worcestershire sauce
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1 tablespoon oil
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1 teaspoon coarse ground black pepper
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½ teaspoon kosher salt
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½ cup very thinly sliced onion
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½ cup very thinly sliced bell peppers
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½ cup button mushrooms, sliced
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For the Cheese Sauce:
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½ tablespoon unsalted butter
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½ cup COLD milk
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½ tablespoon cornstarch
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4 ounces shredded Horseradish Cheddar (or sharp white)
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For the Sandwiches:
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butter for the skillet
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8 slices sourdough bread