German sweet bread with Hazelnut Filling - Nusszopf

Name: German sweet bread with Hazelnut Filling - Nusszopf
Cuisine: European, German
Ingredients: 500g flour; 30g yeast (fresh) or 1 package dry yeast; 1/4l lukewarm milk; 80g butter; 50g sugar; 1 dash salt; zest of ½ organic lemon; Filling; 200g marzipan, raw; 2 egg white; 2 tbsp sugar; 150g ground almonds or hazelnuts (or half/half); 2 cl rum; 4 tbsp powdered sugar; 2 tbsp lemon juice, 2 tbsp water