Make the chocolate filling a day in advance to allow it to properly set.

Heat the whipping cream to a boil and pour it over the chopped dark chocolate.

Gently stir the mixture until all the chocolate is melted and smooth.

Refrigerate the chocolate filling overnight.

Preheat the oven to 375°F (190°C).

Draw eight 8-inch circles on parchment paper and place them on baking sheets.

In a large bowl, whip the egg whites with cream of tartar until stiff peaks form, gradually adding 1/3 cup of sugar.

Set the whipped egg whites aside.

In a separate bowl, whisk the egg yolks with the remaining sugar until the mixture is light and fluffy.

Stir the unsweetened cocoa powder into the boiling water to create a paste.

Slowly add the cocoa paste to the yolk mixture and mix well.

Sift the cake flour and cornstarch over the yolk mixture.

Gently fold in 1/3 of the whipped egg whites into the yolk mixture.

Repeat the folding process with the remaining egg whites.

Spoon 1/2 cup of the cake batter onto each of the drawn circles on the parchment paper.

Bake for 5-8 minutes, or until the cake springs back when touched.

Allow the baked cake circles to cool completely.

To prepare the syrup, combine water and sugar in a saucepan and bring to a boil.

Remove the syrup from the heat and stir in the liqueur of your choice.

Whip the chilled chocolate filling until it is light and airy.

Moisten each cake circle with the prepared syrup.

Spread a generous layer of the chocolate filling over each moistened cake circle.

Stack the cake circles on top of each other, layering with the chocolate filling.

Cover the sides and top of the assembled cake with the remaining chocolate filling.

Sprinkle chocolate curls and shavings over the cake for decoration.

To make the truffles, heat the whipping cream until it is just below a simmer.

Pour the hot cream over the chopped dark chocolate.

Stir gently until the chocolate is melted and the mixture is smooth.

Stir in the liqueur of your choice.

Refrigerate the truffle mixture for about 1 hour, or until it is firm enough to roll into balls.

Spoon small teaspoonfuls of the chocolate mixture and roll them into balls.

Place the chocolate balls on a baking tray and freeze for 30 minutes to harden.

Dip each truffle in melted chocolate, using a toothpick or dipping tools.

Place the coated truffles on a clean tray and allow the chocolate coating to set.

Once the chocolate coating is set, dust the truffles with cocoa powder.