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Lightly oil a small baking sheet.
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Whisk the stock, semolina flour, and salt in a heavy medium saucepan over medium-high heat until the mixture bubbles and is very thick, about 10 minute.
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Beat the egg in a large bowl.
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Gradually beat the semolina mixture into the egg.
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Transfer the gnocchi mixture to the prepared baking sheet, spreading it to form a 1/2-inch thick layer.
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Cover and refrigerate until the gnocchi mixture is cold and firm, at least 1 hour.
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Preheat the broiler.
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Generously butter a 10-inch diameter gratin dish.
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Using a 2" cookie cutter, cut out rounds from the gnocchi mixture.
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Arrange the gnocchi in the prepared baking/gratin dish, overlapping slightly.
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Brush the remaining butter over the gnocchi.
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Sprinkle with the cheese and pepper, if desired.
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Broil until the gnocchi are heated through and beginning to brown, about 6 minute.