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1
Place egg whites in a large bowl; let stand at room temperature 30 minutes. Preheat oven to 350u00b0. Line bottom of a greased 15x10x1-in. baking pan with parchment paper; grease paper. Sift flour, spices and salt together twice.
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2
In a large bowl, beat egg yolks until slightly thickened. Gradually add brown sugar, beating on high speed until thick. Beat in molasses, oil and fresh ginger. Fold in flour mixture (batter will be thick).
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3
Add cream of tartar to egg whites; with clean beaters, beat on medium until soft peaks form. Gradually add sugar, 1 tablespoon at a time, beating after each addition until sugar is dissolved. Beat on high until stiff, glossy peaks form. Using a large whisk, fold a fourth of the whites into batter, then fold in remaining whites. Transfer to prepared pan, spreading evenly.
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4
Bake 10-12 minutes or until top springs back when lightly touched. Cool 5 minutes. Invert onto a tea towel dusted with cocoa. Gently peel off paper. Roll up cake in towel jelly-roll style. Cool completely on a wire rack.
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5
For filling, in a small bowl, mix mascarpone cheese, confectioners' sugar, cream and salt just until blended; stir in ginger. Refrigerate, covered, while preparing bark and buttercream.
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6
For bark, line the underside of a 15x10x1-in. baking pan with parchment paper. Using an offset spatula, spread melted chocolate in a thin, even layer on parchment. Refrigerate until set, about 30 minutes.
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7
For buttercream, place egg whites, sugar and salt in a heatproof bowl; whisk until blended. Place bowl over simmering water in a large saucepan over medium heat. Whisking constantly, heat mixture until a thermometer reads 160u00b0, 1-2 minutes.
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8
Remove from heat. With the whisk attachment of a hand mixer, beat on high speed until stiff glossy peaks form and mixture has cooled, about 5 minutes. Gradually beat in butter, a few tablespoons at a time, on medium speed until smooth. Beat in cooled chocolate.
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9
To assemble, unroll cake; spread filling over cake to within 1/4 in. of edges. Roll up again, without towel; trim ends. Transfer to a platter. Spread buttercream over cake.
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10
To decorate cake, lift chilled chocolate with fingers and break carefully into shards; arrange over buttercream, overlapping slightly. If chocolate becomes too soft, return to refrigerator as necessary.
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11
Refrigerate cake, loosely covered, until serving. Using a serrated knife, cut cake into slices.
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12
Entire cake can be made up to 1 week before serving. Prepare and decorate cake as directed; freeze 2 hours or until firm. Wrap cake in several layers of plastic wrap. Return to freezer; freeze for up to 1 week. To serve, partially thaw wrapped cake in refrigerator overnight. Carefully remove plastic wrap; let cake stand at room temperature 15-30 minutes before serving.
