Beat butter, sugar, and vanilla sugar together for 3 to 5 minutes until light and frothy. Add the eggs one at a time, beating well after each addition. In a separate bowl, combine flour, baking soda, and cinnamon. Fold the dry ingredients into the butter mixture until just combined.
Fold in the nuts and roughly grated apples. Pour the batter into a greased wreath-shaped cake pan.
Smooth the top of the batter. Bake at 170°C (338°F) for about 70 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Allow the cake to cool. Spread or drizzle the cake icing over the cooled wreath cake.