Lightly chop the walnuts, transfer them to a baking sheet and bake at 180 degrees (top/bottom heat) for approximately 8-10 minutes - be careful not to burn them! Set aside to cool.

Break the chocolate into pieces and melt it in a bain-marie - pour a little water into the bottom of a pot and bring it to a boil, place a heatproof bowl with the broken chocolate over the pot and heat it until it melts.

Cool the chocolate.

Cream the softened butter with sugar until fluffy.

Meanwhile, sift the flour together with the baking powder through a sieve.

Add the eggs one by one to the butter mixture, mixing briefly after each addition.

Add the flour to the butter mixture and mix briefly - just until combined.

Add the cooled chocolate to the batter and gently mix.

Finally, add the chopped toasted walnuts (65 g) and mix with a spatula.

Transfer the batter to the prepared pan.

Arrange walnut halves on top.

Bake the cake at 180 degrees (top/bottom heat) for approximately 30-35 minutes - the cake will rise slightly, but then will slightly sink.