Mix the sugar and butter until creamy. Just add the egg yolk (do not dispose of the egg white, it is needed for the coating) and milk and stir everything until smooth. Mix the flour, baking powder, salt and custard powder and sift into the butter mixture. Then stir everything into a crumbly dough with the stirring hook. Divide this and mix one half with the cocoa. Then knead both crumbly doughs by hand and shape each into a 30 cm long roll. Cut both rolls into 15 approx. 1.5 cm portions and roll them into balls.
For the chocolate dough, whip the egg white very lightly until frothy. Pull the balls through briefly, roll them immediately in the chopped nuts and place them on the baking sheet lined with baking paper or foil with a large distance. When everything is in place, press a cork into it with a bottle cork that has always been dipped in cold water and then lightly plate it. Be careful not to tear the resulting edge. Then always place a small portion of the caramel mixture in the wells with two small teaspoons.
Preheat the oven to 170 ° O / bottom heat and slide the tray into the oven on the 2nd rail from below. The baking time is 12-15 minutes. After baking, carefully pull the foil onto a grid and let the cookies cool down on it. When hot, they are still very soft and fragile.
While the chocolate cookies are baking, spread the light-colored balls on another piece of foil already lying on a firm surface, press the hollows in with the cork and fill them with the caramel mixture. Then just press the nut halves in there, after the previous baking process, including the foil, pull them onto the tray and also push them into the oven for 12-15 minutes. With the light cookies you can - depending on your preference - decorate the surface with a little chocolate or couverture after cooling.
The number of people mentioned above relates to a total of 30 pieces.