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1
Position a rack in the lower third of the oven; preheat to 325u00b0F. Meanwhile, to make the cake, line the bottom of the springform pan with parchment paper; grease the sides. Set pan on a wide sheet of heavy-duty foil; wrap foil up sides of pan without tearing it. Set pan in a larger baking pan or a roasting pan. Bring a kettle of water to a boil.
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2
Preferably using a hand-held mixer, beat the eggs at high speed until volume of eggs doubles to about 1 quart, about 5 minutes. If you have to use a heavy-duty mixer, use the whisk attachment and speed 6 and beat to same volume, which will take about the same amount of time. Melt the chocolate and butter, with coffee or liqueur, if using. In a large heatproof bowl, either set in a pan of barely simmering water or in the microwave on medium (50 percent) power, stirring frequently for 4 to 6 minutes or until mixture is smooth and warm (about 115u00b0F).
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3
Fold one-third of egg foam into chocolate mixture with a large rubber spatula until just a few streaks of egg are still visible. Fold in half of the remaining foam in the same way. Fold remaining foam into batter until completely incorporated.
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4
Scrape batter into prepared springform; smooth the surface. Set roasting pan on oven rack; pour enough boiling water into pan to come about halfway up the side of the springform.
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5
Bake until the cake has risen slightly, the edges are just beginning to set, a thin glazed crust (like a brownie) has formed on the surface, and an instant-read thermometer inserted halfway into center of cake registers 140u00b0F, 20 to 25 minutes.
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6
Remove springform from water bath; set on a wire rack and let cool to room temperature. Cover and refrigerate overnight to mellow. Cake can be kept covered and refrigerated up to 4 days.
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7
To make the sauce, if using frozen raspberries, drain them and reserve the juice. Place fresh or drained frozen berries in the bowl of a food processor. Pulse briefly but not until perfectly smooth. Press the puree through a strainer to remove the seeds. Add some of the reserved juice, if desired. If the puree seems too tart, sweeten it to taste. Cover and refrigerate until serving.
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8
About 30 minutes before serving, remove the springform pan sides, invert the cake onto a sheet of waxed paper, peel off the parchment liner, and turn the cake right side up on a serving platter.
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9
To serve, sieve the cake lightly with powdered sugar, if desired. Whip the cream with the vanilla and 2 teaspoons of sugar or more to taste until nearly stiff. Serve slim slices on a pool of raspberry sauce with a dollop of whipped cream on top.
