Place one cake half into loosed bottom cake ring on your serving platter.
Whip the heavy cream with the powder sugar until soft peaks and chill while you make the caramel mix.
Heat the sugar over medium heat until melts and golden brown in color. Add the butter gradually and stir until melted. Take off the heat and add the heavy cream gradually. Set aside to cool completely stirring occasionally.
Fold only 1 cup of the cooled caramel mix. Into the whipped cream and then fold in the ground walnuts. Add 2 tbsp of the walnuts halves and fold again. Pour over the chocolate cake half and smooth the top. Chill for 4-5 hours. Pour the rest of the caramel mixture over the top and sprinkle with the rest of the walnuts halves.