Make the chocolate dough by mixing 400 grams of croissant dough with the cocoa powder and a little water. You need this water because the dough absorbs water due to the cocoa. By adding a little water, the consistency stays the same as regular dough. Mix well until you have a nice brown dough. Roll out the chocolate dough to 3 mm thickness. Roll the normal croissant dough to 20 mm thickness and top with the chocolate dough. Finally roll the dough to the eventual thickness of 3 mm.
Make sure that the layer has wet edges so that the tornados keep their shape when baking. Cut pieces of 7 cm by 30 cm. Then slice them diagonally (see step 1). Place a pipe on the widest part of the dough and then roll out the dough to form a tower. Place the dough in a greased tart case.
Leave the tornados to rise in a proving cabinet at a temperature of 28°C with a humidity of a maximum of 70%, until the dough is nice and loose. Glaze the tornados with egg yolk.
To make the filling, beat the egg yolk with half of the sugar. Add half the milk along with the custard powder. Stir well. In a pan, bring the rest of the milk and cream to the boil. Take the pan from the heat and stir carefully through the mixture. Return to the pan and put back on the heat. Let the mixture simmer gently until the mix reaches the desired thickness. Finally add the chocolate drops. After baking, remove the pipes from the tornados. Leave to cool down and then fill them with the filling.