For the student slices, first prepare the dough. To do this, mix flour, salt and sugar. Cut cold butter into flakes, add and rub finely with your fingers. Add the egg and quickly knead into a firm dough. Chill for at least half an hour.
Grease and flour the baking tray, spread the bottom of the tray with the dough (do not raise the edge), chill again.
To prepare the filling, mix sugar, butter and egg until creamy. Add milk, mix properly. In a separate container, mix baking powder, flour, hazelnuts, cocoa and cinnamon and stir the whole thing with the egg mixture.
Spread the pastry base with the jam and spread the filling on top, smoothing it out. Bake in a heated oven at 200 degrees for 20 to 30 minutes, then let cool.
Break the chocolate into pieces and melt in a water bath. Add butter and powdered sugar and stir until smooth.
Coat the dough with it, let it dry and then cut it into student slices.