Line the bottom of a baking tin of 20 cm with baking paper. Grease the sides with butter.
Grind the walnuts in the bowl. Add the butter and pinch of salt and mix well. Beat the egg yolks with the sugar until the mixture has thickened. Add the walnuts butter mixture and baking powder, vanilla sugar and cinnamon and beat well together. Beat the egg whites until the foam has become peaks.
Fold the egg whites carefully into four parts by the batter.
Pour the batter into the baking tin and bake 60-70 minutes in the oven.
Let the cake cool down at least 30 minutes in the tin.