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1
TO MAKE CAKE: Preheat the oven to 350F (180C).
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With a pastry brush or paper towel, coat an 11x17 inch jelly-roll pan with the butter.
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3
This will seem like a lot; be very generous.
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4
Sprinkle the flour or cocoa over the butter and shake the pan to coat the butter fully.
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5
Tap the edge of the pan on a table to knock out the excess flour.
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6
Melt the chocolate in a double boiler or a bowl over a pan of simmering water.
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Set aside to cool to lukewarm.
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8
Beat the egg whites with a pinch of salt until the whites cling to the beater.
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9
Add about 1/4 cup of the sugar and beat until the whites form stiff, unwavering peaks.
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10
Cream the butter and the other (about) 1/4 cup of the sugar until the mixture is light and fluffy.
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11
Add the melted chocolate and beat in the egg yolks one at a time.
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12
With a rubber spatula, stir about 13 of the beaten egg whites into the chocolate mixture, then pour the chocolate mixture over the rest of the whites.
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13
Sprinkle the flour lightly on top.
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14
Gently fold the mixture together until no white streaks remain.
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15
Pour the batter into the prepared pan, spreading it evenly with a rubber spatula.
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Bake in the middle of the oven for 15 to 18 minutes, or until the cake shrinks slightly away from the sides of the pan and a knife inserted in the middle comes out clean.
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17
It will still be very flat.
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18
Loosen the cake from the pan with a sharp knife around the sides and turn it out onto a rack to cool.
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19
(Put the rack over the pan and flip the whole thing over to keep the cake from breaking. )
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20
TO MAKE FILLING: In a small, heavy saucepan, combine the cream and chocolate and stir over medium heat until the chocolate dissolves.
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Then reduce the heat to very low and simmer, stirring constantly, until the mixture thickens to the consistency of a pudding.
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22
Pour it into a bowl and refrigerate for at least 1 hour.
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23
When the mixture is very cold, pour in the rum and vanilla and beat with a whisk or beater until the filling is smooth and creamy and forms soft peaks when the beater is lifted.
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Do not over-beat or you will get butter.
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25
(If this should happen, don't despair; chocolate buttercream makes a perfectly fine filling. )
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26
Cut the cake in half to make two layers, each about 8 1/2 inches wide.
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Spread the filling over one layer and set the other layer on top.
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28
Smooth out the edges with a spatula.
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29
If one of the cake layers should break, use it on the bottom.
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30
Refrigerate on a rack for about 1 hour.
