Preheat your oven to 425°F.
Grease or line 16 muffin tins with baking paper liners.
In a large bowl, mix together the flour, baking powder, baking soda, salt, and sugar.
In another bowl, whisk the eggs, buttermilk, sour cream, melted butter, oil, and vanilla.
Pour the wet mixture into the dry ingredients and stir with a spatula until almost combined. Add the chocolate chips and mix in.
Cover the bowl with a towel and let the batter rest for 30 minutes (optional, but helps the muffins rise taller).
Fill each muffin cup halfway with batter.
Add 1 teaspoon of Nutella on top of the batter in each muffin cup.
Fill with more batter until the muffin cups are full.
Microwave the remaining Nutella for 5-10 seconds to make it easier to swirl.
Spoon the remaining Nutella on top of the muffins and use a toothpick to gently swirl it around. Sprinkle with extra chocolate chips if you like.