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1
Place rack in center of oven, and heat oven to 350 degrees.
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2
Butter an 11-by-17-inch jelly-roll pan or a 12-by-17 1/2-inch sheet pan, and line with parchment paper.
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3
In a small saucepan, heat 1 cup cream to a simmer.
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4
Add chocolate, reduce heat, and whisk until chocolate is melted.
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5
As soon as mixture is a uniform dark color, remove from heat and let cool for a few minutes.
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6
Whip egg whites and 2 tablespoons sugar to stiff, glossy peaks, about 1 1/2 minutes.
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7
Whisk one-quarter of the egg-white mixture into the chocolate mixture.
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8
Gently fold chocolate mixture back into the original egg-white mixture, and mix until smooth and well combined.
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9
Pour batter into the prepared pan, and spread it in an even layer with a rubber spatula.
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10
Bake until cake is set and puffy, 10 to 12 minutes.
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11
Transfer to a wire rack, and cool to room temperature.
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12
Lift parchment paper to remove cake from pan, and set it on work surface with long side facing edge of table.
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13
Using a fine-mesh sieve, lightly dust cake with cocoa powder.
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14
For the creme chantilly, whip the remaining 1 cup cream with the remaining 1 1/2 tablespoons sugar, the vanilla, and cognac.
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15
Spread evenly over entire surface of cake.
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16
Roll the cake lengthwise, starting at a point 2 to 3 inches over the creme chantilly.
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17
Roll cake another few inches, pressing against parchment paper to make a tight spiral.
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18
Gently peel parchment paper off as cake layer rolls away.
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19
Complete the roll, stopping at the far edge of the parchment paper.
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20
Tuck the loose parchment paper around and underneath the cylinder so it is well wrapped and can be moved easily.
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21
Serve immediately, or refrigerate for up to 4 hours.
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22
When ready to serve, transfer roulade to serving platter.
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23
Remove parchment paper, gently rolling cake into center of platter, with seam on bottom.
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24
(If roll has slumped or twisted, lay a piece of plastic over top and sides, and reshape with hands.) With a sharp knife, trim both ends of roll crosswise or on a diagonal.
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25
Dust top with confectioners' sugar and cocoa powder, and garnish with seasonal fruit.
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26
To serve, cut the roll into 1-inch-thick slices, and lay flat on dessert plates; top with additional creme chantilly if desired.
