Preheat the oven to 425°F, and line the muffin pan cavities with liners.
Whisk all the dry ingredients together, and set aside.
2 cups All-purpose flour, ½ teaspoon Baking powder, 1 teaspoon Baking soda, 1½ teaspoon Pumpkin pie spice, ½ teaspoon Salt
In a separate bowl mix the melted butter, oil, sugar, vanilla, and buttermilk until well combined. Lightly beat the eggs and add them to the mixture.
1 cup Dark brown sugar, ⅓ cup Oil, ⅓ cup Butter, 2 Eggs, ¾ cup Buttermilk, 1 tablespoon Vanilla extract
Add the pumpkin puree and mix.
1 cup Pumpkin puree
Make a well in the center of the dry ingredients and pour the wet mixture in. Gently fold the dry ingredients and mix.
Fill up the muffin liners to almost full. Melt the Nutella in the microwave for 20-second intervals until pourable.
½ cup Nutella
Using a small spoon make a hole in the center of the muffin batter and fill it up with melted Nutella.
With the tip of a pairing knife make swirls in the batter and Nuttela. You can drizzle more Nutella on top.
Bake in the 425°F oven for 5 minutes, then bring the temperature down to 350°F and rotate the pan. Bake for another 9-10 minutes.
Let cool down in the pan then transfer to the cooling rack.