In a large bowl, mix warm water with yeast and 1 tablespoon of the sugar. Let it sit for 5–10 minutes, until it looks foamy.

Add the remaining sugar, flour, salt, egg, and softened butter. Stir until a dough forms, then knead until smooth and elastic, about 8 minutes by hand or mixer.

Cover the bowl with plastic wrap or a clean towel and let the dough rise in a warm spot until it doubles in size, around 1 hour.

Lightly flour a work surface and roll the dough into a 10×14-inch rectangle.

Spread Nutella evenly across the dough, leaving a small border around the edges.

Starting from one long side, roll the dough tightly into a log. Trim the ends if uneven, then cut into 12 even slices.

Place each slice cut-side up into a greased standard muffin tin. Cover loosely and let rise again until puffy, about 45 minutes.

Preheat oven to 350°F. Bake the buns for 15–17 minutes, or until golden brown on top.

While they bake, mix 1/3 cup sugar with the cinnamon in a small bowl.

Let the buns cool slightly in the pan, then remove and roll them in the cinnamon sugar while still warm.