|Sugar||100 Gram (1/2 Cup)|
|Salt||1 1⁄2 Pinch (1 Large Pinch)|
|Lemon||1 , rind grated|
|Flour||100 Gram (3/4 Cup, Roughly)|
|Cornstarch||20 Gram (3 Tablespoon)|
|For the buttercream|
|Sugar||300 Gram (1 1/2 Cups)|
|Water||1⁄8 Liter (1/2 Cup)|
|Semisweet chocolate||3 Ounce (70 Gram, Good Quality)|
|Butter||400 Gram (1 3/4 Cups)|
|Cocoa||50 Gram (1/2 Cup, Generous)|
|Marzipan leaves||4 (For The Garnish)|
|Meringue mushrooms||1 Cup (16 tbs) (For The Garnish)|
Stir together the egg yolks with 1 tablespoon sugar, the salt, and the lemon rind; the mixture should be smooth but not frothy or over-aerated.
Beat the egg whites with the remaining sugar.
Fold the egg yolk mixture into the stiffly beaten whites.
Combine the flour and cornstarch, sift, and carefully stir into the mixture.
Preheat the oven to 425°F. (240°C).
Line a baking sheet with parchment paper or silicone paper and spread the batter evenly over it, preferably with an offset-blade spatula or a cake cutter.
Bake on the center shelf of the oven for about 8-10 minutes, but check after 6 minutes to be sure the sponge layer is not becoming too dark.
When the sponge layer is done, turn it out onto a damp cloth and allow to cool, covered with another cloth.
Boil the sugar and water to the soft-ball stage (240°F./ 116°C).
Beat the egg yolks until very light and foamy, then trickle the sugar syrup down the side of the bowl in a very thin stream, continuing to beat vigorously as you do so.
Melt the chocolate over hot water in a double boiler or bain-marie arrangement.
Cream the butter with the cocoa and chocolate until very light and combine with the egg yolk mixture.
Spread the sponge sheet evenly with half the buttercream, roll up, and very thinly spread the outside with the buttercream.
Spoon the remaining buttercream into a pastry bag fitted with a small star tip and decorate the cake with piped strips of the mixture.
The remaining garnish is up to individual fancy.
The log will yield 16-18 individual slices.