I adapted this recipe from Passionate About Baking. Her adapted cake version is from Baking Obsession and Baking Obsession adapted Alice Medrich's recipe for the Chocolate Genoise.
3 tablespoons clarified butter/ghee
1 teaspoon pure vanilla extract
1/3 cup all-purpose flour
1/3 cup unsweetened Dutch-process cocoa powder
4 large eggs (I used 5 as the eggs were smallish)
2/3 cup fine granulated vanilla sugar
1/4 cup water
1/4 cup sugar
Or espresso powder.
Simmer water and sugar for a few minutes to make the syrup. Add coffee extract or espresso powder.
1 cup Mascarpone
1/4 cup heavy cream ( whipping cream)
1 cup or more Powdered sugar
Optional: I ground a few espresso beans into a very fine powder and added to the mascarpone mixture. You could also use coffee extract.
Shaved chocolate for garnish.
Beat mascarpone with heavy cream (whipping cream) until smooth. Add vanilla (coffee if using) and add powdered sugar. Mix well. Should be thick enough to spread between layers and to ice the cake.
Preheat the oven to 350F. Line, grease & flour an 8-inch round cake pan.
Sift the flour and cocoa together three times; reserve.
Bring some water to a boil in a large pan & reduce to simmer.
Place eggs & sugar in a large bowl, whisk constantly over the simmering
water, heat the eggs to lukewarm (about 105F). Remove the bowl from the
pan; leave the pan on the stove but turn off the heat. With an
electric stand mixer, (I used a Magic Mill) beat the egg mixture at high speed until it has cooled,
tripled in volume, and resembles softly whipped cream, about 5 minutes
in a heavy-duty mixer or longer with a less powerful mixer.
Meanwhile, set the bowl of clarified butter/ghee and vanilla in the
skillet of hot water, with the burner off, to keep it warm.
Sift about one-third of the flour and cocoa over the whipped eggs. Use
a rubber spatula to fold in the mixture-quickly but gently-until
combined. Fold in half the remaining flour and cocoa, then fold in the
rest. Remove the warm butter mixture from the skillet. Scoop about 1
cup of the batter into the bowl with the butter and fold together until
completely combined. Use the large rubber spatula to fold the butter
mixture completely into the remaining batter. Turn the batter into the
prepared pan and tilt to level.
Bake until the cake beginning to shrink slightly around the edges and
the top springs back when pressed with your finger, about 40-45
minutes. Cool the cake completely in the pan on a rack.
To unmold, run a small knife or spatula around the inner edges of the
pan. Invert it onto a rack and remove the parchment liner. Turn the
cake right side up. The génoise can be wrapped and refrigerated for up
to 2 days, or frozen for up to 3 months.
Split cake (I use dental floss to cut through cake)
Brush each layer with coffee syrup. Spread mascarpone filling over
bottom layer. Add top layer and ice with remaining mascarpone. Sprinkle
with shaved chocolate and refrigerate for a few hours before serving.