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1
Making the sugar syrup: Sprinkle the sugar over the bottom of a deep, heavy medium saucepan. Pour the water evenly over the sugar. Over medium-high heat, cook without stirring, tilting the pan gently once or twice to insure that all the sugar is dissolved, until the syrup begins to bubble, 2 to 3 minutes.
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2
Caramelizing the syrup: Cook at a vigorous boil, watching attentively, until the syrup just begins to turn golden, 5 to 6 minutes. Gently move the pan from side to side, without stirring, so the syrup continues to color evenly. Reduce the heat to medium.
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3
Reaching the deeply caramelized stage: Continue to cook the syrup, reducing the heat slightly, until the color becomes a very dark amber and the syrup gives off slight wisps of smoke and smells almost burnt, 1 to 2 minutes longer.
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4
Finishing the sauce: Immediately pour in the cream to stop the cooking. The caramel will bubble up vigorously, so keep your hands clear but do not be alarmed. Immediately reduce the heat to low. Whisk the sauce to blend evenly. Add the butter and simmer a minute or so longer, whisking until smooth.
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5
Serving & storing the sauce: Pour the caramel into a heatproof container. Use immediately or cover and store for up to several days in the refrigerator, where the sauce will thicken as it cools. Reheat gently in a double boiler, in a heavy-bottomed saucepan over very low heat, or in the microwave.
