Instructions for the cake:
Heat oven to 180°C. Line a 20 x 40 cm baking sheet with baking paper. Melt butter in a pan over low heat and then let cool.
Beat eggs and sugar in a bowl. Beat for a long time, until mixture is thickened, twice the volume and filled with tiny bubbles, about 7–10 minutes.
Stir flour, cocoa, instant coffee and salt in another bowl, and gently sift half of the flour into the egg mixture. Gently fold the flour into the egg mixture using a spatula in a figure-eight pattern. Repeat with the second half of the flour.
Add the melted butter around the edges of the bowl and gently stir into the mixture. Pour the mixture into the prepared baking sheet and bake for 15 minutes. Once baked, immediately transfer the cake layer to a new baking sheet and let cool. Slice the cooled cake layer in half.
Instructions for the cream:
Finely chop chocolate and transfer to a bowl. Add one teaspoon butter. Heat cream and espresso in a small pot and bring to the boil.
Pour hot cream over chopped chocolate and leave for 3–4 minutes. Gently mix together cream and chocolate until it forms a smooth mixture. Cool cream well, and then beat with an electric mixer.
Instructions for the glaze:
Place gelatine into a bowl and mix with several tablespoons cold water to soften.
Gently heat water, sugar and cocoa to the boiling point and then remove from heat. Add cream, return to heat and let boil, stirring constantly. Remove from heat, add softened gelatine and let cool.
Assembly and decoration:
Spread the prepared chocolate cream over the first cake layer, and top with the second layer. Slice cake into small pieces, about 3 x 4 cm. Place cake pieces onto a decorating rack, with a clean piece of paper underneath for decorating.
Pour the prepared glaze over the cakes. If necessary, repeat until the cakes are evenly glazed. Decorate with the melted chocolate, chill well and serve.