Warm the milk to body temperature—when dropped on your wrist, it should feel neutral. Pour into a large bowl, sprinkle in the yeast and 1 teaspoon of sugar, and let sit for 5-10 minutes until foamy.

Melt the butter and let it cool slightly. Mix in the eggs and vanilla.

In a large bowl, whisk together the flour, remaining sugar, and salt. Make a well in the center and add the yeast mixture and butter mixture. Stir with a wooden spoon, then knead by hand when it becomes too thick to stir.

Knead on a floured surface for 8-10 minutes until smooth and springy. If sticky, add flour 1 tablespoon at a time.

Place the dough in a lightly oiled bowl, cover with a damp cloth, and let rise in a warm spot for 1 hour until doubled.

While rising, mix softened butter, brown sugar, and cinnamon in a bowl. Slightly warm the Nutella if needed for easy spreading.

Punch down the dough and roll it into an 18×24-inch rectangle about ¼ inch thick.

Spread Nutella evenly, leaving a 1-inch border along one long edge. Spread the cinnamon-sugar butter mixture on top, then sprinkle chopped hazelnuts.

Roll the dough tightly from the filled long edge, then pinch the seam to seal.

Cut into 12 equal rolls using dental floss or a sharp knife. Place in a greased 9×13-inch baking pan with space between each roll.

Let rise for another 30 minutes until puffy. Preheat oven to 350°F.

Bake for 25-30 minutes until golden brown. If browning too fast, tent with foil.

Whisk together powdered sugar, milk, vanilla, and salt for the glaze. It should be thick but pourable.

Let rolls cool for 10 minutes before glazing so it settles without completely melting.