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1
For the Roulade Sponge Cake:
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2
Separate the eggs, reserving all of the yolks and 6 of the whites.
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3
The remaining 6 whites can be stored in the fridge for another purpose.
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4
In the bowl of an electric mixer, whisk the egg yolks with the vanilla and half the sugar until it quadruples in volume and turns pale yellow, about 10 minutes on high speed.
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5
In a separate mixing bowl using a clean whisk attachment, beat the egg whites on medium speed until they start to foam.
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6
Add the cream of tartar and remaining sugar little by little and continue to beat until stiff peaks form, about 10 minutes, to make a meringue.
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7
Preheat the oven to 400F.
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8
Line an 11-by-17 -inch rimmed baking sheet or jelly roll pan with parchment paper and use some of the butter to grease the top and sides of the sheet pan thoroughly.
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Fold one-third of the meringue into the egg yolk mixture, then fold in the rest, until the mixture is no longer streaked with meringue.
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10
Sift the flour over the meringue in two stages, folding gently after each addition.
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11
Pour the batter onto the prepared baking sheet and smooth with an offset spatula.
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Bake for 15 minutes, or until a cake tester inserted in the center of the cake comes out clean and the cake is a pale golden color.
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13
Let the cake cool in the pan, then immediately cover the pan in plastic wrap, so the cake doesnt dry out.
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14
Refrigerate until needed or overnight.
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15
For the Filling:
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In a saucepan, combine the blueberries, orange zest and juice, confectioners sugar, and cornstarch.
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Bring to a boil and reduce the liquid until slightly thickened, about 5 minutes.
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Let cool to room temperature.
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19
To Assemble and Serve:
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Remove the plastic wrap from the pan and slide the cake onto a clean kitchen towel sprinkled with confectioners sugar.
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21
Spread the cooled blueberry filling over the cake so that the filling is thinner at the edges (the filling will spread a little as the cake is rolled).
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22
Starting at a long end of the cake, use the towel to lift the cake from underneath.
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23
Tucking the edge in and peeling away the towel as you go, roll tightly away from you.
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24
Transfer the jelly roll to a flat serving plate, seam side down.
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25
Cut crosswise into 112-inch-thick slices and serve.
