2. In a small bowl, whisk the 1 cup of flour with the cocoa
and salt. In another small bowl, combine the chocolate
and espresso. In the bowl of a standing electric mixer,
combine the egg yolks with 2/3 cup of the sugar. Set the
bowl over a pan of simmering water and whisk until the
sugar is dissolved. Transfer the bowl to the mixer fitted
with the whisk and beat at high speed until the yolks are
pale and thick, about 5 minutes. Beat in the melted
chocolate mixture along with the vanilla. Transfer to a
large bowl.
3. Thoroughly wash and dry the mixer bowl and the
whisk. Beat the egg whites with the cream of tartar on
moderately high speed until soft peaks form. Gradually
add the remaining 2/3 cup of sugar and continue
beating at high speed until the whites are glossy, about 2
minutes longer. Whisk one-fourth of the egg whites into
the cake batter, then fold in the remaining whites until
no streaks remain.
4. In a small bowl, whisk the melted butter with 1/2 cup of
the batter; fold this mixture into the batter. Working in
2 batches, sift the cocoa powder mixture over the batter
and gently fold it in. Divide the batter between the
prepared pans, spreading it out to fill the pans. Bake for
about 18 minutes, until the cake feels springy and dry;
shift the pans from top to bottom and front to back
halfway through baking. Transfer the pans to racks to
cool completely. Run the tip of a knife around the edges,
cover with parchment paper and a baking sheet and
invert; peel off the parchment on top.
5. Spread the Malted Buttercream over the cakes. Using a
ruler, cut each cake precisely in half lengthwise, cutting
13