20 ounces milk chocolate, cut into 1/4-inch pieces
4 ounces bittersweet chocolate, cut into 1/4-inch pieces
Butter two 9-inch round pans, 1 1/2 to 2 inches deep, and line with buttered
parchment or wax paper. Set a rack at the middle level of the oven and preheat
to 350 degrees F.
Cake: Sift the cake flour, baking powder and salt onto a piece of parchment or
wax paper and set aside.
Using an electric mixer set at medium speed, beat the butter and sugar until
light, about 3 minutes.
Beat in the lemon zest and extract.
In a bowl, whisk together the egg whites and milk.
Add a third of the flour mixture to the butter and sugar mixture and beat
until smooth. Scrape down bowl and beaters.
Beat in half the milk and egg white
mixture until incorporated, then beat in another third of the flour mixture.
Scrape bowl and beaters.
Beat in remaining liquid until absorbed, followed by
remaining flour mixture. Scrape well after each addition.
Divide batter between prepared pans and smooth top evenly.
Bake for about 30 to 35 minutes, until well risen and a wooden pick inserted
in the center emerges clean.
Cool layers in pans for 5 minutes, then invert to racks to cool.
Peel off paper. If prepared in advance, double-wrap layers in plastic wrap
and chill for up to several days or freeze.
Milk Chocolate Ganache: Place the pieces of zest in a saucepan and add the
cream. Place over low heat and bring to a simmer. Remove from heat and allow
to steep about 5 minutes.
Remove zests from cream with a slotted spoon and discard them.
Add butter to the cream and bring to a boil over low heat.
Remove from heat and add chocolates. Shake pan to submerge chocolate and allow to stand
Whisk smooth, then cool to room temperature. Ganache will thicken
to spreading consistency.
To finish, put one layer right side up on a platter or cardboard. Place
ganache in mixer bowl and beat until light, about 20 seconds. Using an offset
spatula, spread the layer with about a third of the ganache. Place the other
cake layer upside down on the ganache, so that the smooth bottom of the cake
layer is uppermost. Spread the top and sides of the cake evenly with most of
the remaining ganache, but save about 1/2 to 1/3 cup to pipe decorations on
top of the cake.
After smoothing the outside of cake, use a pastry bag fitted with a medium
star tube and pipe a series of rosettes around the top rim of the cake.
Storage: Keep the cake at a cool room temperature before serving.
Keep leftovers under a cake dome at a cool room temperature or covered with plastic wrap in