Whisk the granulated sugar and vegetable oil together in a large bowl until combined.

Whisk in the eggs and vanilla extract until smooth, then slowly stream in the buttermilk. Whisk until combined.

Fold the all purpose flour, baking powder, and salt into the wet ingredients with a rubber spatula just until most of the flour is incorporated. Add the chocolate chips and continue folding just until no dry streaks remain.

Let the batter rest at room temperature while the oven preheats to 425°F. Line your muffin pan by placing paper liners in every other cup to give the muffins space to rise. Fill each liner all the way to the top with batter.

Transfer the Nutella to a piping bag fitted with a round tip or a zip-top bag with the corner snipped off. Insert the tip into the center of each muffin and pipe a generous amount of Nutella into the batter. If desired, add a small swirl of Nutella on top and sprinkle with extra chocolate chips.

Bake the muffins at 425°F for 5 minutes, then reduce the temperature to 350°F and continue baking for 10-13 minutes. The muffins are done when the tops are domed and set, and a toothpick inserted near the edge (not directly into the Nutella center) comes out with a few moist crumbs attached.

Let the muffins cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.