Preheat the oven to 350° F (180° C/160° C convection). Remove all ingredients from the refrigerator ahead of time, they should be room temperature.
Grease a loaf pan with butter. Also grease a sheet of parchment paper and line the pan with it. This helps to prevent the cake from breaking when it comes out.
For the batter, beat the butter with a hand mixer until fluffy. Gradually add the sugar and vanilla sugar, beating all the time. Gradually add the eggs to the bowl. Be sure to beat each egg well before adding the next.
In another bowl, mix all the dry ingredients together, such as the nuts, flour, baking powder, and any other spices. Do not add all of the chopped hazelnuts to the batter, save some for later.
Then stir the dry ingredients into the wet ingredients in the bowl. Add the lukewarm milk and mix just until you have a homogeneous mixture.
Pour the batter into the prepared loaf pan and smooth it down. Place the pan in the preheated oven and bake for about 50 to 60 minutes.
Test the cake with a wooden skewer or toothpick to determine if it is done. There should be no sticky batter sticking to a wooden stick in the center of the cake.
Remove the cake from the oven and let it cool in the pan before removing the parchment paper.
Meanwhile, prepare the glaze. Heat the store-bought hazelnut glaze according to instructions and spread it generously over the cooled cake, sprinkling the remaining chopped hazelnuts on top.You can also pour melted chocolate glaze over the top or serve without the glaze.