Pre-heat the oven to 220 °C and line a 12-cup muffin tin with paper liners.
In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, pumpkin pie spice, and a pinch of salt. Set aside.
In a large mixing bowl, combine the pumpkin purée and both sugars (granulated and light brown). Then, whisk in the oil, eggs, vanilla extract, and sour cream until smooth and well-blended.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
Fill each muffin liner with the batter, filling them up to the rim for a nice rise.
Place a tsp of Nutella on top of each muffin. Use a toothpick or skewer to swirl it into the batter, ensuring the chocolate spreads throughout for a beautiful marbled effect.
Bake in the preheated oven for 5 minutes , then lower the temperature to 180 degrees and continue baking for the rest of the time or until a toothpick inserted into the center comes out clean, with just a few moist crumbs attached.
