Sift the flour and set aside.
Beat the 2 whole eggs and 2 egg yolks with the scant ½ cup (2 ¾ oz./80 g) sugar until the mixture is pale and thick.
Whisk the 2 egg whites with the 2 ½ tablespoons (1 oz./30 g) sugar to soft peaks.
Carefully fold the whisked egg whites into the first mixture and pour in the sifted flour.
Stir until just combined. Spread the batter out onto the pan and bake for about 5–7 minutes.
It should be only very lightly colored. When cooled, leave at room temperature.
Prepare the whipped chocolate-hazelnut ganache
Chop the chocolate and melt it slowly in a bain-marie or in the microwave oven (on “defrost” or at 500 W maximum, stirring from time to time). Add the praline.
Bring the ⅔ cup (160 ml) whipping cream to the boil. Gradually pour one-third of the boiling cream over the melted chocolate and praline.
Using a flexible spatula, mix it in energetically, drawing small circles to create an elastic, shiny “kernel.”
Incorporate the second third of the cream, using the same procedure. Repeat with the last third.
Stir in the remaining 1 ⅔ cups (400 ml) cold cream. Process until the mixture is smooth and thoroughly emulsified.
Chill for at least 3 hours, and then whip the ganache at medium speed until it is creamy. If you whip it any faster, it will lose its light, creamy texture and will become fatty.
Turn the jelly roll sponge out of the pan. Spread one-third of the ganache over it and sprinkle with a few roughly chopped hazelnuts. Roll up the sponge and cover completely with the remaining whipped ganache.
Decorate with roasted chopped hazelnuts and dust with confectioners’ sugar.
This recipe is from Cooking With Chocolate, published by Flammarion, out now.