Heat the oven to 180˚ C (350˚F). Bruise the cardamom pods and remove the black seeds. Throw away the green shells and ground the black seeds in the pestle and mortar.
Mix the butter with the sugar and mix till you have a lightly colored creamy mixture. Whisk the eggs together in a separate bowl and add them to your butter mixture in three stages. Mix in between each egg until fully incorporated.
Put the flour and cocoa powder through a sieve above your bowl. Add the hazelnuts directly and mix everything together with a wooden spoon gently. Stir in the milk together with the ground cardamom seeds and the chopped chocolate pieces.
Grease your cake tin well and dust with flour. Tap out the excess flour and put the batter into the form. Put it into the oven for 50 mins. Take the cake out of the oven (after checking if it is fully cooked) and leave to cool in the tin for about 15 mins. Then turn out onto a cooling rack and leave to cool for a further 45 mins before starting your decorating.
For the sauce you can put the chocolate and the butter together in a bowl and melt it in a double boiler above softly boiling water. Make sure the bottom of your bowl does not touch the water. Once it is all melted, leave to let it cool a little bit. You want it to firm up a tiny bit before you pour it over the cake. Finish with the chopped pistachio's.