Take a bowl and add the granulated sugar, the butter cut into pieces (which must be cold from the refrigerator) and the vanilla extract. Knead, with the help of a fork so as not to overheat the butter, and then add the egg. A compact cream should be obtained.

Add the previously sifted cocoa to the bowl; add the flour, potato starch and yeast, also sieved, and continue to knead with a fork.

Once you have reached a compact consistency, continue to knead with your hands on a work surface.

Once you have created the smooth shortcrust pastry, let it cool in the refrigerator for at least 2 hours wrapped in cling film or in an airtight bowl.

To create the coffee and chocolate cream, heat a saucepan with the milk inside and the vanilla extract on the stove.

In a bowl, pour the egg yolks and the granulated sugar; mix the ingredients with the help of a whisk.

Add the sifted cornstarch and continue beating until creamy smooth and without lumps.

At this point, add the milk previously heated on the fire to the mixture created.

Mix all the ingredients with a whisk for a few more seconds.

Place the saucepan with the liquids on the heat and cook for about 4/5 minutes, or in any case until the cream is no longer firm. Keep aside.

To reproduce the chocolate ganache, take a saucepan and put the cream and dark chocolate inside it: let the ingredients melt over very low heat, turning them constantly to prevent them from sticking to the bottom.

Once the chocolate has melted, add the instant coffee and mix well.

Set aside a little bit of this thick cream just obtained for the final decoration. Now combine the remaining chocolate ganache with the cream created previously.

Mix the mixture well and set aside.

At this point, recover the cooled pastry, place it on a work surface and, with the help of a rolling pin, roll it out to a thickness of about 4 mm.

Line a 24 cm diameter pan with parchment paper (or greased and floured) and prick the base with the tines of a fork. Pour the chocolate and coffee cream inside and bake in a static oven for about 40 minutes at 170 °. After this time, take it out of the oven and let it cool completely.

To create the white chocolate ganache, take a saucepan and pour the cream and white chocolate into it. Allow the ingredients to melt over low heat until you have a smooth cream and set aside for the final decoration.

Retrieve the dark chocolate ganache kept aside and place it inside a piping bag.

Take the cooled shortcrust pastry and fill it with the melted white chocolate ganache.

Leave the tart to cool down for about 20 minutes. Then start with the dark chocolate decoration by creating circles on its surface.

Take a toothpick and divide the cream into four wedges; start from the center of the cake and drag the wooden toothpick outwards.

For each wedge created, perform the opposite movement: from the outside of the cake stretch the toothpick inwards.

In this way, the final decoration of the mocaccina cake will be obtained with the classic shape of a cobweb.