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1
Prepare a 1 quart souffle dish by creating a collar to go around the rim to support the souffle while it freezes; cut a sheet of waxed paper long enough to go around the dish's rim, then fold in thirds, lengthwise (about a 4 inch wide ribbon).
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2
It should extend about 3 inches above the rim; secure with a rubber band or tape (or you could prepare 8 ramekins with the collar 1 1/2 inches above each one).
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3
In a large saucepan, over medium heat, cook the blackberries and 1/3 cup sugar until they soften and burst, about 10 minutes; puree in a food processor, then strain the seeds out (you should have about 2 cups of puree).
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4
Stir in the liquer and chill.
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5
In a small saucepan, heat remaining 2/3 cup sugar and water, over medium heat, to the soft-ball stage, 235 - 240 degrees, about 15 minutes.
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6
Stir until the sugar dissolves, then stop stirring, but use a small brush, moistened with water, to wash down any crystal that may form on the sides of the pan.
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7
Meanwhile, beat the egg whites in a stand mixer, using the whisk attachment, until stiff peaks form; while running pour the sugar mixture, in a slow steady stream, into the egg whites taking care not to hit the whisk attachment and splatter.
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8
The egg whites will swell, then subside; continue beating until the egg whites cool to room temperature, about 8 minutes.
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9
In a large bowl, beat the whipping cream, until soft peaks form, using a whisk or hand mixer.
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10
Stir 1/3 of the egg white mixture into the blackberry puree, then pour the blackberry mixture into the remaining egg whites and gently fold until well combined.
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11
Gently fold the whipping cream into the egg whites, then spoon the mixture into the prepared souffle dish or the ramekins; it should come about 1/2 up the waxed paper collar.
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12
Smooth the top and freeze until very firm, 4 hours to overnight; if frozen overnight, it will need and hour in the refrigerator before serving.
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13
If freezing for more than a day, press plastic wrap onto the surface once it is frozen to store.
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14
To serve, remove the collar and cut into thin slices.
