Prepare the Dough:
In a large mixing bowl, combine the warm milk, yeast, and sugar. Stir gently and let it sit for about 5 minutes, or until the mixture becomes frothy.
Add the melted butter and egg to the yeast mixture and whisk until combined.
Gradually add the flour and salt, mixing until a soft dough forms.
Knead the dough on a floured surface for about 5-7 minutes, or until smooth and elastic.
Place the dough in a greased bowl, cover with a clean cloth, and let it rise in a warm place for about 1 hour, or until doubled in size.
Prepare the Filling:
In a small bowl, mix together the softened butter, brown sugar, and cinnamon until well combined.
Roll Out the Dough:
After the dough has risen, punch it down and turn it out onto a lightly floured surface.
Roll the dough into a large rectangle, about 16x12 inches.
Add the Filling:
Spread the chocolate hazelnut spread evenly over the dough, leaving a small border around the edges.
Spread the cinnamon-sugar mixture on top of the chocolate hazelnut spread.
Sprinkle the chopped hazelnuts evenly over the filling, if using.
Roll and Cut the Dough:
Starting from the long edge, tightly roll the dough into a log.
Cut the log into 12 even slices using a sharp knife or dough cutter.
Place the rolls in a greased 9x13 inch baking dish.
Second Rise:
Cover the baking dish with a clean cloth and let the rolls rise for an additional 30 minutes, or until puffy.
Bake the Rolls:
Preheat your oven to 350°F (175°C).
Bake the rolls for 25-30 minutes, or until they are golden brown and cooked through.
Prepare the Glaze:
While the rolls are baking, whisk together the powdered sugar, milk or cream, and vanilla extract until smooth. Adjust the consistency with more milk or sugar as needed.
Glaze and Serve:
Once the rolls are baked, remove them from the oven and let them cool for a few minutes.
Drizzle the glaze over the warm rolls and serve.